diff --git a/backend/app/administration.go b/backend/app/administration.go
index 8c02172..8b16c20 100644
--- a/backend/app/administration.go
+++ b/backend/app/administration.go
@@ -53,11 +53,17 @@ const (
 	ROUTE_V1_USER_SESSIONS            = "/api/v1/user/sessions"
 	ROUTE_V1_USER_SESSIONS_INVALIDATE = "/api/v1/user/sessions/invalidate"
 	ROUTE_V1_USER_API                 = "/api/v1/user/api"
-	// sso
+	// sso — legacy entra id (kept for backwards compatibility)
 	ROUTE_V1_SSO_ENTRA_ID          = "/api/v1/sso/entra-id"
 	ROUTE_V1_SSO_ENTRA_ID_ENABLED  = "/api/v1/sso/entra-id/enabled"
 	ROUTE_V1_SSO_ENTRA_ID_LOGIN    = "/api/v1/sso/entra-id/login"
 	ROUTE_V1_SSO_ENTRA_ID_CALLBACK = "/api/v1/sso/entra-id/auth"
+	// sso — generic oidc
+	ROUTE_V1_SSO_OIDC_ENABLED  = "/api/v1/sso/oidc/enabled"
+	ROUTE_V1_SSO_OIDC_LOGIN    = "/api/v1/sso/oidc/login"
+	ROUTE_V1_SSO_OIDC_CALLBACK = "/api/v1/sso/oidc/auth"
+	// sso — combined status (true when either provider is active)
+	ROUTE_V1_SSO_ANY_ENABLED = "/api/v1/sso/enabled"
 	// mfa
 	ROUTE_V1_USER_MFA_TOTP_SETUP        = "/api/v1/user/mfa/totp/setup"
 	ROUTE_V1_USER_MFA_TOTP_SETUP_VERIFY = "/api/v1/user/mfa/totp/setup/verify"
@@ -287,11 +293,17 @@ func setupRoutes(
 		GET(ROUTE_V1_USER_API, middleware.SessionHandler, controllers.User.GetMaskedAPIKey).
 		POST(ROUTE_V1_USER_API, middleware.SessionHandler, controllers.User.UpsertAPIKey).
 		DELETE(ROUTE_V1_USER_API, middleware.SessionHandler, controllers.User.RemoveAPIKey).
-		// sso
-		GET(ROUTE_V1_SSO_ENTRA_ID_ENABLED, controllers.SSO.IsEnabled).
+		// sso — legacy entra id
+		GET(ROUTE_V1_SSO_ENTRA_ID_ENABLED, controllers.SSO.IsLegacyEnabled).
 		POST(ROUTE_V1_SSO_ENTRA_ID, middleware.SessionHandler, controllers.SSO.Upsert).
 		GET(ROUTE_V1_SSO_ENTRA_ID_LOGIN, controllers.SSO.EntreIDLogin).
 		GET(ROUTE_V1_SSO_ENTRA_ID_CALLBACK, controllers.SSO.EntreIDCallBack).
+		// sso — generic oidc
+		GET(ROUTE_V1_SSO_OIDC_ENABLED, controllers.SSO.IsOIDCEnabled).
+		GET(ROUTE_V1_SSO_OIDC_LOGIN, controllers.SSO.OIDCLogin).
+		GET(ROUTE_V1_SSO_OIDC_CALLBACK, controllers.SSO.OIDCCallback).
+		// sso — combined
+		GET(ROUTE_V1_SSO_ANY_ENABLED, controllers.SSO.IsEnabled).
 		// user mfa
 		GET(ROUTE_V1_USER_MFA_TOTP, middleware.SessionHandler, controllers.User.IsTOTPEnabled).
 		POST(ROUTE_V1_USER_MFA_TOTP_SETUP, middleware.LoginRateLimiter, middleware.SessionHandler, controllers.User.SetupTOTP).
diff --git a/backend/app/services.go b/backend/app/services.go
index 6051caf..eda78ce 100644
--- a/backend/app/services.go
+++ b/backend/app/services.go
@@ -2,6 +2,7 @@ package app
 
 import (
 	"github.com/caddyserver/certmagic"
+	"github.com/phishingclub/phishingclub/repository"
 	"github.com/phishingclub/phishingclub/service"
 	"go.uber.org/zap"
 	"gorm.io/gorm"
@@ -100,6 +101,7 @@ func NewServices(
 		RoleRepository:    repositories.Role,
 		CompanyRepository: repositories.Company,
 		PasswordHasher:    utilities.PasswordHasher,
+		OptionRepository:  repositories.Option,
 	}
 	recipient := &service.Recipient{
 		Common:                      common,
@@ -228,7 +230,8 @@ func NewServices(
 		OptionsService: optionService,
 		UserService:    userService,
 		SessionService: sessionService,
-		// MSALClient:     msalClient, this dependency is set AFTER this function
+		SSOStateRepo:   &repository.SSOState{DB: db},
+		// MSALClient and OIDCClient are set AFTER this function on startup
 	}
 	backupService := &service.Backup{
 		Common:        common,
diff --git a/backend/controller/sso.go b/backend/controller/sso.go
index 273c71a..7f9c68f 100644
--- a/backend/controller/sso.go
+++ b/backend/controller/sso.go
@@ -41,15 +41,24 @@ func (s *SSO) Upsert(g *gin.Context) {
 	s.Response.OK(g, gin.H{})
 }
 
+// IsEnabled reports whether any SSO provider (legacy Entra ID or generic OIDC)
+// is currently active.
 func (s *SSO) IsEnabled(g *gin.Context) {
-	// if no sso client is setup, then it is not enabled
-	if s.SSO.MSALClient == nil {
-		s.Response.OK(g, false)
-		return
-	}
-	s.Response.OK(g, true)
+	s.Response.OK(g, s.SSO.IsEnabled())
 }
 
+// IsLegacyEnabled reports whether the legacy Microsoft Entra ID path is active.
+func (s *SSO) IsLegacyEnabled(g *gin.Context) {
+	s.Response.OK(g, s.SSO.IsLegacyEnabled())
+}
+
+// IsOIDCEnabled reports whether the generic OIDC path is active.
+func (s *SSO) IsOIDCEnabled(g *gin.Context) {
+	s.Response.OK(g, s.SSO.IsOIDCEnabled())
+}
+
+// EntreIDLogin initiates the legacy Microsoft Entra ID login flow by
+// redirecting the browser to the Microsoft authorization endpoint.
 func (s *SSO) EntreIDLogin(g *gin.Context) {
 	authURL, err := s.SSO.EntreIDLogin(g)
 	if errors.Is(err, errs.ErrSSODisabled) {
@@ -63,6 +72,8 @@ func (s *SSO) EntreIDLogin(g *gin.Context) {
 	g.Redirect(http.StatusTemporaryRedirect, authURL)
 }
 
+// EntreIDCallBack handles the authorization code callback from Microsoft for
+// the legacy Entra ID flow.
 func (s *SSO) EntreIDCallBack(g *gin.Context) {
 	code := g.Query("code")
 	session, err := s.SSO.HandlEntraIDCallback(g, code)
@@ -73,7 +84,71 @@ func (s *SSO) EntreIDCallBack(g *gin.Context) {
 	if ok := s.handleErrors(g, err); !ok {
 		return
 	}
-	// Set the session in the cookie
+	setSessionCookie(g, session)
+	g.Redirect(http.StatusTemporaryRedirect, "/dashboard")
+}
+
+// OIDCLogin initiates the generic OIDC login flow by generating a PKCE pair,
+// persisting the state record and redirecting the browser to the provider's
+// authorization endpoint.
+func (s *SSO) OIDCLogin(g *gin.Context) {
+	authURL, err := s.SSO.OIDCLoginURL(g.Request.Context())
+	if errors.Is(err, errs.ErrSSODisabled) {
+		s.Response.BadRequest(g)
+		return
+	}
+	if ok := s.handleErrors(g, err); !ok {
+		s.Response.BadRequest(g)
+		return
+	}
+	g.Redirect(http.StatusTemporaryRedirect, authURL)
+}
+
+// OIDCCallback handles the authorization code callback from a generic OIDC
+// provider.  It validates the state token (CSRF), completes the PKCE token
+// exchange, verifies the nonce, enforces role and ACR requirements, then
+// creates or reuses a local account and sets a session cookie.
+func (s *SSO) OIDCCallback(g *gin.Context) {
+	code := g.Query("code")
+	state := g.Query("state")
+	errorParam := g.Query("error")
+
+	// surface provider-level errors without leaking detail to the user
+	if errorParam != "" {
+		errDesc := g.Query("error_description")
+		s.Logger.Warnw("oidc provider returned error on callback",
+			"error", errorParam,
+			"description", errDesc,
+		)
+		g.Redirect(http.StatusTemporaryRedirect, "/login?ssoAuthError=1")
+		return
+	}
+
+	if code == "" || state == "" {
+		s.Logger.Warnw("oidc callback missing required parameters")
+		g.Redirect(http.StatusTemporaryRedirect, "/login?ssoAuthError=1")
+		return
+	}
+
+	session, err := s.SSO.HandleOIDCCallback(
+		g.Request.Context(),
+		code,
+		state,
+		g.ClientIP(),
+	)
+	if err != nil {
+		s.Logger.Warnw("oidc callback failed", "error", err)
+		g.Redirect(http.StatusTemporaryRedirect, "/login?ssoAuthError=1")
+		return
+	}
+
+	setSessionCookie(g, session)
+	g.Redirect(http.StatusTemporaryRedirect, "/dashboard")
+}
+
+// setSessionCookie writes the session ID into a secure, HttpOnly, SameSite=Strict
+// cookie on the response.
+func setSessionCookie(g *gin.Context, session *model.Session) {
 	cookie := &http.Cookie{
 		Name:     data.SessionCookieKey,
 		Value:    session.ID.String(),
@@ -84,5 +159,4 @@ func (s *SSO) EntreIDCallBack(g *gin.Context) {
 		Expires:  *session.MaxAgeAt,
 	}
 	http.SetCookie(g.Writer, cookie)
-	g.Redirect(http.StatusTemporaryRedirect, "/dashboard")
 }
diff --git a/backend/database/ssoState.go b/backend/database/ssoState.go
new file mode 100644
index 0000000..3454344
--- /dev/null
+++ b/backend/database/ssoState.go
@@ -0,0 +1,47 @@
+package database
+
+import "time"
+
+const (
+	SSO_STATE_TABLE = "sso_states"
+)
+
+// SSOState stores short-lived state tokens for the generic OIDC login flow.
+// Each record ties together the CSRF state token, the PKCE code verifier and
+// an optional nonce so that the callback handler can verify the round-trip and
+// complete the token exchange securely.
+type SSOState struct {
+	// ID is a random UUID primary key.
+	ID string `gorm:"primary_key;not null;unique;type:varchar(36)"`
+
+	// StateToken is the value sent as the OAuth2 'state' parameter.
+	// It is compared on callback to prevent CSRF attacks.
+	StateToken string `gorm:"not null;uniqueIndex;type:varchar(255)"`
+
+	// CodeVerifier is the plain-text PKCE verifier (RFC 7636).
+	// The SHA-256 hash of this value was sent to the provider as the
+	// code_challenge during the authorization request.
+	CodeVerifier string `gorm:"not null;type:varchar(255)"`
+
+	// Nonce is the OIDC nonce embedded in the id_token claim.
+	// It is verified after token exchange to prevent replay attacks.
+	Nonce string `gorm:"not null;type:varchar(255)"`
+
+	// CreatedAt is the creation timestamp.
+	CreatedAt *time.Time `gorm:"not null;index"`
+
+	// ExpiresAt is when this record should be considered invalid.
+	// State tokens are valid for 10 minutes.
+	ExpiresAt *time.Time `gorm:"not null;index"`
+
+	// Used marks the token as consumed so it cannot be replayed.
+	Used bool `gorm:"not null;default:false;index"`
+
+	// UsedAt is the time the token was consumed.
+	UsedAt *time.Time `gorm:"index"`
+}
+
+// TableName returns the table name for gorm.
+func (SSOState) TableName() string {
+	return SSO_STATE_TABLE
+}
diff --git a/backend/go.mod b/backend/go.mod
index 0d91aae..d1efd26 100644
--- a/backend/go.mod
+++ b/backend/go.mod
@@ -49,6 +49,7 @@ require (
 	github.com/charmbracelet/x/term v0.2.1 // indirect
 	github.com/cloudwego/base64x v0.1.4 // indirect
 	github.com/cloudwego/iasm v0.2.0 // indirect
+	github.com/coreos/go-oidc/v3 v3.17.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/enetx/g v1.0.194 // indirect
 	github.com/enetx/http v1.0.19 // indirect
@@ -61,6 +62,7 @@ require (
 	github.com/gaukas/clienthellod v0.4.2 // indirect
 	github.com/gaukas/godicttls v0.0.4 // indirect
 	github.com/gin-contrib/sse v0.1.0 // indirect
+	github.com/go-jose/go-jose/v4 v4.1.3 // indirect
 	github.com/go-playground/locales v0.14.1 // indirect
 	github.com/go-playground/universal-translator v0.18.1 // indirect
 	github.com/go-playground/validator/v10 v10.22.0 // indirect
@@ -106,6 +108,7 @@ require (
 	go.uber.org/multierr v1.11.0 // indirect
 	golang.org/x/arch v0.9.0 // indirect
 	golang.org/x/exp v0.0.0-20251023183803-a4bb9ffd2546 // indirect
+	golang.org/x/oauth2 v0.28.0 // indirect
 	golang.org/x/sys v0.37.0 // indirect
 	golang.org/x/text v0.30.0 // indirect
 	golang.org/x/tools v0.38.0 // indirect
diff --git a/backend/go.sum b/backend/go.sum
index e90a2da..dbfc570 100644
--- a/backend/go.sum
+++ b/backend/go.sum
@@ -42,6 +42,8 @@ github.com/cloudwego/base64x v0.1.4 h1:jwCgWpFanWmN8xoIUHa2rtzmkd5J2plF/dnLS6Xd/
 github.com/cloudwego/base64x v0.1.4/go.mod h1:0zlkT4Wn5C6NdauXdJRhSKRlJvmclQ1hhJgA0rcu/8w=
 github.com/cloudwego/iasm v0.2.0 h1:1KNIy1I1H9hNNFEEH3DVnI4UujN+1zjpuk6gwHLTssg=
 github.com/cloudwego/iasm v0.2.0/go.mod h1:8rXZaNYT2n95jn+zTI1sDr+IgcD2GVs0nlbbQPiEFhY=
+github.com/coreos/go-oidc/v3 v3.17.0 h1:hWBGaQfbi0iVviX4ibC7bk8OKT5qNr4klBaCHVNvehc=
+github.com/coreos/go-oidc/v3 v3.17.0/go.mod h1:wqPbKFrVnE90vty060SB40FCJ8fTHTxSwyXJqZH+sI8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -85,6 +87,8 @@ github.com/gkampitakis/go-snaps v0.5.15 h1:amyJrvM1D33cPHwVrjo9jQxX8g/7E2wYdZ+01
 github.com/gkampitakis/go-snaps v0.5.15/go.mod h1:HNpx/9GoKisdhw9AFOBT1N7DBs9DiHo/hGheFGBZ+mc=
 github.com/go-errors/errors v1.5.1 h1:ZwEMSLRCapFLflTpT7NKaAc7ukJ8ZPEjzlxt8rPN8bk=
 github.com/go-errors/errors v1.5.1/go.mod h1:sIVyrIiJhuEF+Pj9Ebtd6P/rEYROXFi3BopGUQ5a5Og=
+github.com/go-jose/go-jose/v4 v4.1.3 h1:CVLmWDhDVRa6Mi/IgCgaopNosCaHz7zrMeF9MlZRkrs=
+github.com/go-jose/go-jose/v4 v4.1.3/go.mod h1:x4oUasVrzR7071A4TnHLGSPpNOm2a21K9Kf04k1rs08=
 github.com/go-logr/logr v1.4.3 h1:CjnDlHq8ikf6E492q6eKboGOC0T8CDaOvkHCIg8idEI=
 github.com/go-logr/logr v1.4.3/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
 github.com/go-playground/assert/v2 v2.2.0 h1:JvknZsQTYeFEAhQwI4qEt9cyV5ONwRHC+lYKSsYSR8s=
@@ -266,6 +270,8 @@ golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug
 golang.org/x/net v0.7.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
 golang.org/x/net v0.46.0 h1:giFlY12I07fugqwPuWJi68oOnpfqFnJIJzaIIm2JVV4=
 golang.org/x/net v0.46.0/go.mod h1:Q9BGdFy1y4nkUwiLvT5qtyhAnEHgnQ/zd8PfU6nc210=
+golang.org/x/oauth2 v0.28.0 h1:CrgCKl8PPAVtLnU3c+EDw6x11699EWlsDeWNWKdIOkc=
+golang.org/x/oauth2 v0.28.0/go.mod h1:onh5ek6nERTohokkhCD/y2cV4Do3fxFHFuAejCkRWT8=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.18.0 h1:kr88TuHDroi+UVf+0hZnirlk8o8T+4MrK6mr60WkH/I=
diff --git a/backend/main.go b/backend/main.go
index a989268..294bda5 100644
--- a/backend/main.go
+++ b/backend/main.go
@@ -232,19 +232,35 @@ func main() {
 		certMagicCache,
 		*flagFilePath,
 	)
-	// get entra-id options and setup msal client
+	// initialise sso clients based on the stored configuration
 	ssoOpt, err := services.SSO.GetSSOOptionWithoutAuth(context.Background())
 	if err != nil {
-		logger.Errorw("failed to setup sso", "error", err)
+		logger.Errorw("failed to load sso configuration", "error", err)
 		return
 	}
 	if ssoOpt.Enabled {
-		services.SSO.MSALClient, err = sso.NewEntreIDClient(ssoOpt)
-		if err != nil && !errors.Is(err, errs.ErrSSODisabled) {
-			logger.Errorw("failed to setup msal client", "error", err)
-			return
+		if ssoOpt.IsLegacyEntraID() {
+			// legacy microsoft entra id path via msal
+			services.SSO.MSALClient, err = sso.NewEntreIDClient(ssoOpt)
+			if err != nil && !errors.Is(err, errs.ErrSSODisabled) {
+				logger.Errorw("failed to setup msal client", "error", err)
+				return
+			}
+		} else if ssoOpt.IsOIDC() {
+			// generic oidc path
+			services.SSO.OIDCClient, err = sso.NewOIDCClient(
+				context.Background(),
+				ssoOpt.IssuerURL.String(),
+				ssoOpt.ClientID.String(),
+				ssoOpt.ClientSecret.String(),
+				ssoOpt.RedirectURL.String(),
+				[]string{"openid", "profile", "email"},
+			)
+			if err != nil {
+				// log but do not abort startup — operator can reconfigure via the ui
+				logger.Errorw("failed to setup oidc client, sso will be unavailable", "error", err)
+			}
 		}
-
 	}
 	middlewares := app.NewMiddlewares(
 		1,
diff --git a/backend/model/ssoOption.go b/backend/model/ssoOption.go
index 89dddc2..e944a02 100644
--- a/backend/model/ssoOption.go
+++ b/backend/model/ssoOption.go
@@ -12,24 +12,107 @@ import (
 	"github.com/phishingclub/phishingclub/vo"
 )
 
+// SSOOption holds all SSO configuration.
+//
+// Legacy Entra ID fields (ClientID, TenantID, ClientSecret, RedirectURL) are
+// preserved so existing installations continue to work without any admin
+// intervention.  When TenantID is non-empty the system treats the config as a
+// legacy Entra ID installation and uses the MSAL path.
+//
+// For new generic OIDC providers the operator sets IssuerURL together with the
+// shared ClientID / ClientSecret / RedirectURL fields and leaves TenantID
+// empty.
 type SSOOption struct {
-	Enabled      bool                  `json:"enabled"`
-	ClientID     vo.OptionalString64   `json:"clientID"`
-	TenantID     vo.OptionalString64   `json:"tenantID"`
+	// --- shared fields (legacy + oidc) ---
+
+	Enabled bool `json:"enabled"`
+
+	// ClientID is the OAuth2 / OIDC application client id
+	ClientID vo.OptionalString64 `json:"clientID"`
+
+	// ClientSecret is the OAuth2 / OIDC application client secret
 	ClientSecret vo.OptionalString1024 `json:"clientSecret"`
-	RedirectURL  vo.OptionalString1024 `json:"redirectURL"`
+
+	// RedirectURL is the callback URL registered with the provider
+	RedirectURL vo.OptionalString1024 `json:"redirectURL"`
+
+	// --- legacy entra id fields ---
+
+	// TenantID is the Azure AD tenant identifier.
+	// Non-empty value indicates that this is a legacy Entra ID configuration.
+	TenantID vo.OptionalString64 `json:"tenantID"`
+
+	// --- generic oidc fields ---
+
+	// IssuerURL is the OIDC provider issuer, e.g.
+	// "https://keycloak.example.com/realms/myrealm"
+	// The library appends /.well-known/openid-configuration automatically.
+	IssuerURL vo.OptionalString1024 `json:"issuerURL"`
+
+	// --- authorization ---
+
+	// RequiredRoleClaim is the JWT / userinfo claim name that contains the
+	// user's roles, e.g. "roles", "groups", "realm_access.roles".
+	// Empty means role-checking is disabled.
+	RequiredRoleClaim vo.OptionalString255 `json:"requiredRoleClaim"`
+
+	// RequiredRoleValue is the value that must appear inside the claim
+	// identified by RequiredRoleClaim before login is permitted.
+	RequiredRoleValue vo.OptionalString255 `json:"requiredRoleValue"`
+
+	// --- access policy ---
+
+	// SSOOnly disables local username/password login when true.
+	// Admins should ensure at least one SSO-capable account exists before
+	// enabling this to avoid lockout.
+	SSOOnly bool `json:"ssoOnly"`
+
+	// --- acr ---
+
+	// ACRValues is the space-separated list of Authentication Context Class
+	// Reference values to request from the provider, e.g. "urn:mfa".
+	// Empty means no ACR is requested.
+	ACRValues vo.OptionalString255 `json:"acrValues"`
 }
 
+// IsLegacyEntraID returns true when the configuration describes a legacy
+// Microsoft Entra ID (Azure AD) setup identified by a non-empty TenantID.
+func (s *SSOOption) IsLegacyEntraID() bool {
+	return s.TenantID.String() != ""
+}
+
+// IsOIDC returns true when the configuration describes a generic OIDC provider.
+func (s *SSOOption) IsOIDC() bool {
+	return s.IssuerURL.String() != "" && !s.IsLegacyEntraID()
+}
+
+// HasRoleGating returns true when role-based login gating is configured.
+func (s *SSOOption) HasRoleGating() bool {
+	return s.RequiredRoleClaim.String() != "" && s.RequiredRoleValue.String() != ""
+}
+
+// HasACR returns true when an ACR value is configured.
+func (s *SSOOption) HasACR() bool {
+	return s.ACRValues.String() != ""
+}
+
+// NewSSOOptionDefault returns a zeroed SSOOption ready to be stored.
 func NewSSOOptionDefault() *SSOOption {
 	return &SSOOption{
-		Enabled:      false,
-		ClientID:     *vo.NewEmptyOptionalString64(),
-		TenantID:     *vo.NewEmptyOptionalString64(),
-		ClientSecret: *vo.NewEmptyOptionalString1024(),
-		RedirectURL:  *vo.NewEmptyOptionalString1024(),
+		Enabled:           false,
+		ClientID:          *vo.NewEmptyOptionalString64(),
+		TenantID:          *vo.NewEmptyOptionalString64(),
+		ClientSecret:      *vo.NewEmptyOptionalString1024(),
+		RedirectURL:       *vo.NewEmptyOptionalString1024(),
+		IssuerURL:         *vo.NewEmptyOptionalString1024(),
+		RequiredRoleClaim: *vo.NewEmptyOptionalString255(),
+		RequiredRoleValue: *vo.NewEmptyOptionalString255(),
+		SSOOnly:           false,
+		ACRValues:         *vo.NewEmptyOptionalString255(),
 	}
 }
 
+// NewSSOOptionFromJSON unmarshals a JSON blob into an SSOOption.
 func NewSSOOptionFromJSON(jsonData []byte) (*SSOOption, error) {
 	option := &SSOOption{}
 	err := json.Unmarshal(jsonData, option)
@@ -44,6 +127,7 @@ func NewSSOOptionFromJSON(jsonData []byte) (*SSOOption, error) {
 	return option, nil
 }
 
+// NewSSOOptionFromOption converts a generic Option row into an SSOOption.
 func NewSSOOptionFromOption(option *Option) (*SSOOption, error) {
 	if option == nil {
 		return nil, fmt.Errorf("option cannot be nil")
@@ -60,10 +144,12 @@ func NewSSOOptionFromOption(option *Option) (*SSOOption, error) {
 	return ssooption, nil
 }
 
+// ToJSON serialises the SSOOption to JSON.
 func (l *SSOOption) ToJSON() ([]byte, error) {
 	return json.Marshal(l)
 }
 
+// ToOption converts the SSOOption into a generic Option row for persistence.
 func (l *SSOOption) ToOption() (*Option, error) {
 	json, err := l.ToJSON()
 	if err != nil {
diff --git a/backend/repository/ssoState.go b/backend/repository/ssoState.go
new file mode 100644
index 0000000..8aab67c
--- /dev/null
+++ b/backend/repository/ssoState.go
@@ -0,0 +1,116 @@
+package repository
+
+import (
+	"context"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/phishingclub/phishingclub/database"
+	"github.com/phishingclub/phishingclub/errs"
+	"gorm.io/gorm"
+)
+
+// SSOState is the repository for SSO PKCE/CSRF state tokens.
+type SSOState struct {
+	DB *gorm.DB
+}
+
+// SSOStateRecord is a plain struct used to pass state data between
+// the service layer and this repository without importing the database
+// package in the service.
+type SSOStateRecord struct {
+	ID           string
+	StateToken   string
+	CodeVerifier string
+	Nonce        string
+	ExpiresAt    *time.Time
+	Used         bool
+	UsedAt       *time.Time
+}
+
+// Insert persists a new SSO state record and returns its ID.
+func (r *SSOState) Insert(
+	ctx context.Context,
+	stateToken string,
+	codeVerifier string,
+	nonce string,
+	expiresAt *time.Time,
+) (string, error) {
+	id := uuid.New().String()
+	now := time.Now()
+	record := &database.SSOState{
+		ID:           id,
+		StateToken:   stateToken,
+		CodeVerifier: codeVerifier,
+		Nonce:        nonce,
+		CreatedAt:    &now,
+		ExpiresAt:    expiresAt,
+		Used:         false,
+	}
+	if err := r.DB.WithContext(ctx).Create(record).Error; err != nil {
+		return "", errs.Wrap(err)
+	}
+	return id, nil
+}
+
+// GetByStateToken retrieves an unexpired, unused state record by its
+// state token value.  Returns gorm.ErrRecordNotFound when no match exists.
+func (r *SSOState) GetByStateToken(
+	ctx context.Context,
+	stateToken string,
+) (*SSOStateRecord, error) {
+	now := time.Now()
+	var record database.SSOState
+	err := r.DB.WithContext(ctx).
+		Where("state_token = ? AND used = ? AND expires_at > ?", stateToken, false, now).
+		First(&record).Error
+	if err != nil {
+		return nil, errs.Wrap(err)
+	}
+	return toSSOStateRecord(&record), nil
+}
+
+// MarkAsUsed marks the record with the given ID as consumed so it cannot
+// be replayed.
+func (r *SSOState) MarkAsUsed(
+	ctx context.Context,
+	id string,
+) error {
+	now := time.Now()
+	err := r.DB.WithContext(ctx).
+		Model(&database.SSOState{}).
+		Where("id = ?", id).
+		Updates(map[string]any{
+			"used":    true,
+			"used_at": &now,
+		}).Error
+	if err != nil {
+		return errs.Wrap(err)
+	}
+	return nil
+}
+
+// DeleteExpired removes all records whose expiry time has passed.
+func (r *SSOState) DeleteExpired(ctx context.Context) error {
+	now := time.Now()
+	err := r.DB.WithContext(ctx).
+		Where("expires_at < ?", now).
+		Delete(&database.SSOState{}).Error
+	if err != nil {
+		return errs.Wrap(err)
+	}
+	return nil
+}
+
+// toSSOStateRecord maps a database row to the plain repository record type.
+func toSSOStateRecord(d *database.SSOState) *SSOStateRecord {
+	return &SSOStateRecord{
+		ID:           d.ID,
+		StateToken:   d.StateToken,
+		CodeVerifier: d.CodeVerifier,
+		Nonce:        d.Nonce,
+		ExpiresAt:    d.ExpiresAt,
+		Used:         d.Used,
+		UsedAt:       d.UsedAt,
+	}
+}
diff --git a/backend/seed/migrate.go b/backend/seed/migrate.go
index ce2169b..ee26c66 100644
--- a/backend/seed/migrate.go
+++ b/backend/seed/migrate.go
@@ -12,6 +12,7 @@ import (
 	"github.com/phishingclub/phishingclub/database"
 	"github.com/phishingclub/phishingclub/errs"
 	"github.com/phishingclub/phishingclub/model"
+	"github.com/phishingclub/phishingclub/vo"
 	"go.uber.org/zap"
 	"gorm.io/gorm"
 )
@@ -57,6 +58,7 @@ func initialInstallAndSeed(
 		&database.CampaignStats{},
 		&database.OAuthProvider{},
 		&database.OAuthState{},
+		&database.SSOState{},
 	}
 
 	// disable foreign key constraints temporarily for sqlite to allow table recreation
@@ -134,6 +136,73 @@ func initialInstallAndSeed(
 			errors.Errorf("failed to run data migrations: %w", err),
 		)
 	}
+	// migrate legacy entra id config to include derived oidc issuer url
+	err = migrateLegacyEntraIDToOIDC(db, logger)
+	if err != nil {
+		return errs.Wrap(
+			errors.Errorf("failed to migrate legacy entra id sso config: %w", err),
+		)
+	}
+	return nil
+}
+
+// migrateLegacyEntraIDToOIDC inspects the sso_login option row and, when it
+// contains a legacy Entra ID configuration (tenantID present, issuerURL absent),
+// derives a standards-compliant OIDC issuer URL from the tenantID and writes it
+// back.  The tenantID field is preserved so IsLegacyEntraID() continues to
+// return true and the MSAL client path remains active — the issuerURL is
+// stored purely for informational purposes and future reference.
+//
+// This migration is idempotent: running it multiple times on an already-
+// migrated row is safe.
+func migrateLegacyEntraIDToOIDC(db *gorm.DB, logger *zap.SugaredLogger) error {
+	var opt database.Option
+	res := db.Where("key = ?", data.OptionKeyAdminSSOLogin).First(&opt)
+	if res.Error != nil {
+		if strings.Contains(res.Error.Error(), "record not found") {
+			// no sso option yet — nothing to migrate
+			return nil
+		}
+		return errs.Wrap(res.Error)
+	}
+
+	ssoOpt, err := model.NewSSOOptionFromJSON([]byte(opt.Value))
+	if err != nil {
+		// corrupted value — skip migration, do not fail startup
+		logger.Warnw("sso migration: failed to parse sso_login option, skipping", "error", err)
+		return nil
+	}
+
+	// only migrate when tenantID is set and issuerURL is still empty
+	if ssoOpt.TenantID.String() == "" || ssoOpt.IssuerURL.String() != "" {
+		return nil
+	}
+
+	// construct the standard OIDC issuer URL for Azure AD / Entra ID
+	// https://learn.microsoft.com/en-us/entra/identity-platform/v2-protocols-oidc
+	issuer := "https://login.microsoftonline.com/" + ssoOpt.TenantID.String() + "/v2.0"
+	issuerVO, err := vo.NewOptionalString1024(issuer)
+	if err != nil {
+		logger.Warnw("sso migration: failed to build issuer URL VO", "issuer", issuer, "error", err)
+		return nil
+	}
+	ssoOpt.IssuerURL = *issuerVO
+
+	updated, err := ssoOpt.ToJSON()
+	if err != nil {
+		return errs.Wrap(err)
+	}
+
+	res = db.Model(&database.Option{}).
+		Where("key = ?", data.OptionKeyAdminSSOLogin).
+		Update("value", string(updated))
+	if res.Error != nil {
+		return errs.Wrap(res.Error)
+	}
+
+	logger.Infow("sso migration: derived issuerURL from tenantID for legacy Entra ID config",
+		"issuer", issuer,
+	)
 	return nil
 }
 
diff --git a/backend/service/option.go b/backend/service/option.go
index f13f9fe..1f2e259 100644
--- a/backend/service/option.go
+++ b/backend/service/option.go
@@ -77,14 +77,16 @@ func (o *Option) GetOptionWithoutAuth(
 	return opt, nil
 }
 
-// MaskSSOSecret masks the sso secret
+// MaskSSOSecret masks the sso secret before returning the option to callers.
+// The ClientSecret field is zeroed so it is never sent over the wire.
+// All other fields, including the new OIDC and policy fields, are preserved.
 func (o *Option) MaskSSOSecret(opt *model.Option) (*model.Option, error) {
 	a, err := model.NewSSOOptionFromJSON([]byte(opt.Value.String()))
 	if err != nil {
 		o.Logger.Errorw("failed to read sso option", "error", err)
 		return nil, errs.Wrap(err)
 	}
-	// mask the key
+	// zero the secret — never returned over the api
 	a.ClientSecret = *vo.NewOptionalString1024Must("")
 	b, err := a.ToJSON()
 	if err != nil {
diff --git a/backend/service/sso.go b/backend/service/sso.go
index 2a759f1..ddd3321 100644
--- a/backend/service/sso.go
+++ b/backend/service/sso.go
@@ -16,34 +16,46 @@ import (
 	"github.com/phishingclub/phishingclub/data"
 	"github.com/phishingclub/phishingclub/errs"
 	"github.com/phishingclub/phishingclub/model"
+	"github.com/phishingclub/phishingclub/repository"
 	"github.com/phishingclub/phishingclub/sso"
 	"github.com/phishingclub/phishingclub/vo"
 )
 
+// SSO is the service responsible for all single-sign-on operations.
+// It supports two authentication paths:
+//
+//  1. Legacy Microsoft Entra ID (MSAL) — activated when the stored
+//     SSOOption has a non-empty TenantID.
+//  2. Generic OIDC — activated when the stored SSOOption has a non-empty
+//     IssuerURL and an empty TenantID.
 type SSO struct {
 	Common
 	OptionsService *Option
 	UserService    *User
 	SessionService *Session
+	SSOStateRepo   *repository.SSOState
 	MSALClient     *confidential.Client
+	OIDCClient     *sso.OIDCClient
 }
 
+// MsGraphUserInfo is the subset of Microsoft Graph /me fields we care about.
 type MsGraphUserInfo struct {
-	DisplayName       string `json:"displayName"`       // Full name
-	Email             string `json:"mail"`              // Primary email
-	UserPrincipalName string `json:"userPrincipalName"` // Often email or login
-	GivenName         string `json:"givenName"`         // First name
-	Surname           string `json:"surname"`           // Last name
-	ID                string `json:"id"`                // Unique Azure AD ID
+	DisplayName       string `json:"displayName"`
+	Email             string `json:"mail"`
+	UserPrincipalName string `json:"userPrincipalName"`
+	GivenName         string `json:"givenName"`
+	Surname           string `json:"surname"`
+	ID                string `json:"id"`
 }
 
-// Get is the auth protected method for getting SSO details
+// --- read helpers ---
+
+// Get is the auth-protected method for fetching SSO details.
 func (s *SSO) Get(
 	ctx context.Context,
 	session *model.Session,
 ) (*model.SSOOption, error) {
 	ae := NewAuditEvent("SSO.Get", session)
-	// check permissions
 	isAuthorized, err := IsAuthorized(session, data.PERMISSION_ALLOW_GLOBAL)
 	if err != nil && !errors.Is(err, errs.ErrAuthorizationFailed) {
 		s.LogAuthError(err)
@@ -56,57 +68,8 @@ func (s *SSO) Get(
 	return s.GetSSOOptionWithoutAuth(ctx)
 }
 
-// Upsert upserts SSO config it also replaces the in memory SSO configuration
-func (s *SSO) Upsert(
-	ctx context.Context,
-	session *model.Session,
-	ssoOpt *model.SSOOption,
-) error {
-	ae := NewAuditEvent("SSO.Upsert", session)
-	// check permissions
-	isAuthorized, err := IsAuthorized(session, data.PERMISSION_ALLOW_GLOBAL)
-	if err != nil && !errors.Is(err, errs.ErrAuthorizationFailed) {
-		s.LogAuthError(err)
-		return errs.Wrap(err)
-	}
-	if !isAuthorized {
-		s.AuditLogNotAuthorized(ae)
-		return errs.ErrAuthorizationFailed
-	}
-	ssoOpt.Enabled = len(ssoOpt.ClientID.String()) > 0 &&
-		len(ssoOpt.TenantID.String()) > 0 &&
-		len(ssoOpt.ClientSecret.String()) > 0
-
-	// if the config is incomplete, we clear it
-	if !ssoOpt.Enabled {
-		ssoOpt.ClientID = *vo.NewEmptyOptionalString64()
-		ssoOpt.TenantID = *vo.NewEmptyOptionalString64()
-		ssoOpt.ClientSecret = *vo.NewEmptyOptionalString1024()
-		ssoOpt.RedirectURL = *vo.NewEmptyOptionalString1024()
-	}
-	opt, err := ssoOpt.ToOption()
-	if err != nil {
-		return errs.Wrap(err)
-	}
-	err = s.OptionsService.SetOptionByKey(ctx, session, opt)
-	if err != nil {
-		s.Logger.Errorw("failed to upsert sso option", "error", err)
-		return errs.Wrap(err)
-	}
-	s.AuditLogAuthorized(ae)
-	// replace the in memory msal client
-	if ssoOpt.Enabled {
-		s.MSALClient, err = sso.NewEntreIDClient(ssoOpt)
-		if err != nil {
-			return errs.Wrap(err)
-		}
-	} else {
-		s.MSALClient = nil
-	}
-
-	return nil
-}
-
+// GetSSOOptionWithoutAuth reads the SSOOption from the options store without
+// requiring a session.  Used on startup and in public login-flow handlers.
 func (s *SSO) GetSSOOptionWithoutAuth(ctx context.Context) (*model.SSOOption, error) {
 	opt, err := s.OptionsService.GetOptionWithoutAuth(ctx, data.OptionKeyAdminSSOLogin)
 	if err != nil {
@@ -123,18 +86,125 @@ func (s *SSO) GetSSOOptionWithoutAuth(ctx context.Context) (*model.SSOOption, er
 	return ssoOpt, nil
 }
 
+// --- write helper ---
+
+// Upsert persists the SSO configuration and hot-swaps the in-memory clients.
+func (s *SSO) Upsert(
+	ctx context.Context,
+	session *model.Session,
+	ssoOpt *model.SSOOption,
+) error {
+	ae := NewAuditEvent("SSO.Upsert", session)
+	isAuthorized, err := IsAuthorized(session, data.PERMISSION_ALLOW_GLOBAL)
+	if err != nil && !errors.Is(err, errs.ErrAuthorizationFailed) {
+		s.LogAuthError(err)
+		return errs.Wrap(err)
+	}
+	if !isAuthorized {
+		s.AuditLogNotAuthorized(ae)
+		return errs.ErrAuthorizationFailed
+	}
+
+	// determine whether the supplied config is complete enough to enable SSO
+	hasLegacyFields := ssoOpt.ClientID.String() != "" &&
+		ssoOpt.TenantID.String() != "" &&
+		ssoOpt.ClientSecret.String() != ""
+	hasOIDCFields := ssoOpt.ClientID.String() != "" &&
+		ssoOpt.IssuerURL.String() != "" &&
+		ssoOpt.ClientSecret.String() != "" &&
+		ssoOpt.RedirectURL.String() != ""
+
+	ssoOpt.Enabled = hasLegacyFields || hasOIDCFields
+
+	// clear everything when the config is incomplete
+	if !ssoOpt.Enabled {
+		ssoOpt.ClientID = *vo.NewEmptyOptionalString64()
+		ssoOpt.TenantID = *vo.NewEmptyOptionalString64()
+		ssoOpt.ClientSecret = *vo.NewEmptyOptionalString1024()
+		ssoOpt.RedirectURL = *vo.NewEmptyOptionalString1024()
+		ssoOpt.IssuerURL = *vo.NewEmptyOptionalString1024()
+		ssoOpt.RequiredRoleClaim = *vo.NewEmptyOptionalString255()
+		ssoOpt.RequiredRoleValue = *vo.NewEmptyOptionalString255()
+		ssoOpt.ACRValues = *vo.NewEmptyOptionalString255()
+		ssoOpt.SSOOnly = false
+	}
+
+	opt, err := ssoOpt.ToOption()
+	if err != nil {
+		return errs.Wrap(err)
+	}
+	if err = s.OptionsService.SetOptionByKey(ctx, session, opt); err != nil {
+		s.Logger.Errorw("failed to upsert sso option", "error", err)
+		return errs.Wrap(err)
+	}
+	s.AuditLogAuthorized(ae)
+
+	// hot-swap in-memory clients
+	s.MSALClient = nil
+	s.OIDCClient = nil
+	if ssoOpt.Enabled {
+		if ssoOpt.IsLegacyEntraID() {
+			s.MSALClient, err = sso.NewEntreIDClient(ssoOpt)
+			if err != nil {
+				return errs.Wrap(err)
+			}
+		} else if ssoOpt.IsOIDC() {
+			s.OIDCClient, err = sso.NewOIDCClient(
+				ctx,
+				ssoOpt.IssuerURL.String(),
+				ssoOpt.ClientID.String(),
+				ssoOpt.ClientSecret.String(),
+				ssoOpt.RedirectURL.String(),
+				[]string{"openid", "profile", "email"},
+			)
+			if err != nil {
+				return errs.Wrap(err)
+			}
+		}
+	}
+	return nil
+}
+
+// --- status helpers ---
+
+// IsEnabled returns true when either the legacy MSAL client or the generic
+// OIDC client is initialised.
+func (s *SSO) IsEnabled() bool {
+	return s.MSALClient != nil || s.OIDCClient != nil
+}
+
+// IsLegacyEnabled returns true when only the MSAL client is active.
+func (s *SSO) IsLegacyEnabled() bool {
+	return s.MSALClient != nil
+}
+
+// IsOIDCEnabled returns true when the generic OIDC client is active.
+func (s *SSO) IsOIDCEnabled() bool {
+	return s.OIDCClient != nil
+}
+
+// IsSSOOnly reports whether local-password login has been disabled.
+func (s *SSO) IsSSOOnly(ctx context.Context) (bool, error) {
+	opt, err := s.GetSSOOptionWithoutAuth(ctx)
+	if err != nil {
+		return false, err
+	}
+	return opt.SSOOnly && opt.Enabled, nil
+}
+
+// --- legacy Entra ID ---
+
+// EntreIDLogin returns the Microsoft authorization URL for the legacy MSAL
+// flow.  Returns errs.ErrSSODisabled when the MSAL client is not configured.
 func (s *SSO) EntreIDLogin(ctx context.Context) (string, error) {
-	// check if sso is enabled
 	ssoOpt, err := s.GetSSOOptionWithoutAuth(ctx)
 	if err != nil {
 		return "", err
 	}
 	if !ssoOpt.Enabled {
-		s.Logger.Debugf("SSO login URL visited but it is disabed")
+		s.Logger.Debugf("SSO login URL visited but it is disabled")
 		return "", errs.Wrap(errs.ErrSSODisabled)
 	}
-	// the MSALCLient is set on application start up
-	// and when a upsert is done, replacing the old client with new details
 	if s.MSALClient == nil {
 		return "", errs.Wrap(errors.New("no MSAL client"))
 	}
@@ -150,7 +220,8 @@ func (s *SSO) EntreIDLogin(ctx context.Context) (string, error) {
 	return authURL, nil
 }
 
-// EntreIDCallBack checks if the callback is OK then requests user details from the graph API
+// HandlEntraIDCallback completes the legacy Entra ID OAuth2 code exchange,
+// fetches the user from MS Graph and creates (or reuses) a local account.
 func (s *SSO) HandlEntraIDCallback(
 	g *gin.Context,
 	code string,
@@ -179,24 +250,20 @@ func (s *SSO) HandlEntraIDCallback(
 		s.Logger.Debugw("failed to get /me graph info", "error", err)
 		return nil, err
 	}
-	// validate required fields
 	if userInfo.Email == "" && userInfo.UserPrincipalName == "" {
 		err := errors.New("no email provided from SSO")
 		s.Logger.Debugw("no email or userPrincipalName from SSO", "error", err)
 		return nil, errs.Wrap(err)
 	}
-	// determine email (prefer mail over UPN)
 	email := userInfo.Email
 	if email == "" {
 		email = userInfo.UserPrincipalName
 	}
-	// determine name
 	name := userInfo.DisplayName
 	if name == "" {
 		name = strings.TrimSpace(fmt.Sprintf("%s %s", userInfo.GivenName, userInfo.Surname))
 	}
 	if name == "" {
-		// Fallback to email prefix if no name available
 		name = strings.Split(email, "@")[0]
 	}
 	userID, err := s.UserService.CreateFromSSO(g, name, email, userInfo.ID)
@@ -206,7 +273,6 @@ func (s *SSO) HandlEntraIDCallback(
 	if userID == nil {
 		return nil, errs.Wrap(errors.New("user ID is unexpectedly nil"))
 	}
-	// get the user and create a session
 	user, err := s.UserService.GetByIDWithoutAuth(g, userID)
 	if err != nil {
 		s.Logger.Debugf("failed to get SSO user", "error", err)
@@ -221,14 +287,11 @@ func (s *SSO) HandlEntraIDCallback(
 }
 
 func (s *SSO) getMsGraphMe(ctx context.Context, accessToken string) (*MsGraphUserInfo, error) {
-	client := &http.Client{
-		Timeout: 10 * time.Second,
-	}
-	req, err := http.NewRequestWithContext(ctx, "GET", "https://graph.microsoft.com/v1.0/me", nil)
+	client := &http.Client{Timeout: 10 * time.Second}
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, "https://graph.microsoft.com/v1.0/me", nil)
 	if err != nil {
 		return nil, errs.Wrap(err)
 	}
-
 	req.Header.Add("Authorization", fmt.Sprintf("Bearer %s", accessToken))
 
 	resp, err := client.Do(req)
@@ -240,25 +303,194 @@ func (s *SSO) getMsGraphMe(ctx context.Context, accessToken string) (*MsGraphUse
 	if resp.StatusCode != http.StatusOK {
 		return nil, errs.Wrap(fmt.Errorf("graph API returned status %d", resp.StatusCode))
 	}
-
-	// Read and log raw response
 	body, err := io.ReadAll(resp.Body)
 	if err != nil {
 		return nil, errs.Wrap(err)
 	}
-	s.Logger.Debugw("Raw Microsoft Graph response", "body", string(body))
+	s.Logger.Debugw("raw Microsoft Graph response", "body", string(body))
 
 	var userInfo MsGraphUserInfo
 	if err := json.Unmarshal(body, &userInfo); err != nil {
 		return nil, errs.Wrap(err)
 	}
-
-	s.Logger.Debugw("Parsed user info",
+	s.Logger.Debugw("parsed user info",
 		"id", userInfo.ID,
 		"email", userInfo.Email,
 		"displayName", userInfo.DisplayName,
 		"userPrincipalName", userInfo.UserPrincipalName,
 	)
-
 	return &userInfo, nil
 }
+
+// --- generic OIDC ---
+
+// OIDCLoginURL generates the authorization URL for the generic OIDC flow.
+// It creates a PKCE pair, a state token and a nonce, persists them in
+// sso_states and returns the authorization URL.
+func (s *SSO) OIDCLoginURL(ctx context.Context) (string, error) {
+	ssoOpt, err := s.GetSSOOptionWithoutAuth(ctx)
+	if err != nil {
+		return "", err
+	}
+	if !ssoOpt.Enabled || !ssoOpt.IsOIDC() {
+		return "", errs.Wrap(errs.ErrSSODisabled)
+	}
+	if s.OIDCClient == nil {
+		return "", errs.Wrap(errors.New("OIDC client not initialised"))
+	}
+
+	// generate PKCE pair
+	codeVerifier, codeChallenge, err := sso.GeneratePKCEPair()
+	if err != nil {
+		return "", errs.Wrap(err)
+	}
+
+	// generate CSRF state token and nonce
+	state, err := sso.GenerateStateToken()
+	if err != nil {
+		return "", errs.Wrap(err)
+	}
+	nonce, err := sso.GenerateStateToken()
+	if err != nil {
+		return "", errs.Wrap(err)
+	}
+
+	// persist state so the callback can verify and retrieve the verifier
+	expiry := time.Now().Add(sso.SSOStateExpiry)
+	if _, err = s.SSOStateRepo.Insert(ctx, state, codeVerifier, nonce, &expiry); err != nil {
+		return "", errs.Wrap(err)
+	}
+
+	authURL := s.OIDCClient.AuthCodeURL(state, nonce, codeChallenge, ssoOpt.ACRValues.String())
+	return authURL, nil
+}
+
+// HandleOIDCCallback completes the generic OIDC authorisation code flow with
+// PKCE, enforces role and ACR requirements, then creates or reuses a local
+// user account and returns a new session.
+func (s *SSO) HandleOIDCCallback(
+	ctx context.Context,
+	code string,
+	stateToken string,
+	clientIP string,
+) (*model.Session, error) {
+	ssoOpt, err := s.GetSSOOptionWithoutAuth(ctx)
+	if err != nil {
+		return nil, err
+	}
+	if !ssoOpt.Enabled || !ssoOpt.IsOIDC() {
+		return nil, errs.Wrap(errs.ErrSSODisabled)
+	}
+	if s.OIDCClient == nil {
+		return nil, errs.Wrap(errors.New("OIDC client not initialised"))
+	}
+
+	// look up and validate the state record
+	stateRecord, err := s.SSOStateRepo.GetByStateToken(ctx, stateToken)
+	if err != nil {
+		s.Logger.Warnw("oidc callback: state token not found or expired", "error", err)
+		return nil, errs.Wrap(errors.New("invalid or expired state token"))
+	}
+
+	// mark it consumed immediately to prevent replay
+	if err = s.SSOStateRepo.MarkAsUsed(ctx, stateRecord.ID); err != nil {
+		return nil, errs.Wrap(err)
+	}
+
+	// exchange code → tokens (includes id_token signature + nonce verification)
+	result, err := s.OIDCClient.ExchangeCode(ctx, code, stateRecord.CodeVerifier, stateRecord.Nonce)
+	if err != nil {
+		s.Logger.Warnw("oidc token exchange failed", "error", err)
+		return nil, errs.Wrap(err)
+	}
+
+	// --- ACR verification ---
+	if ssoOpt.HasACR() {
+		rawClaims := result.RawClaims
+		acrClaim, _ := rawClaims["acr"].(string)
+		requiredACR := strings.TrimSpace(ssoOpt.ACRValues.String())
+		// the ACR values field may contain multiple space-separated values;
+		// we require that the returned acr matches at least one of them
+		matched := false
+		for _, v := range strings.Fields(requiredACR) {
+			if acrClaim == v {
+				matched = true
+				break
+			}
+		}
+		if !matched {
+			s.Logger.Warnw("oidc acr mismatch",
+				"required", requiredACR,
+				"got", acrClaim,
+			)
+			return nil, errs.Wrap(errors.New("ACR requirement not satisfied"))
+		}
+	}
+
+	// --- role gating ---
+	if ssoOpt.HasRoleGating() {
+		if !sso.CheckRoleClaim(
+			result.RawClaims,
+			ssoOpt.RequiredRoleClaim.String(),
+			ssoOpt.RequiredRoleValue.String(),
+		) {
+			s.Logger.Warnw("oidc login denied: required role not present",
+				"claim", ssoOpt.RequiredRoleClaim.String(),
+				"required", ssoOpt.RequiredRoleValue.String(),
+			)
+			return nil, errs.Wrap(errs.ErrAuthorizationFailed)
+		}
+	}
+
+	// --- fetch user identity ---
+	sub, email, name, err := s.OIDCClient.UserInfoEmail(ctx, result.AccessToken)
+	if err != nil {
+		// fall back to id_token claims on userinfo failure
+		s.Logger.Warnw("oidc userinfo failed, falling back to id_token claims", "error", err)
+		sub = result.IDToken.Subject
+		if v, ok := result.RawClaims["email"].(string); ok {
+			email = v
+		}
+		if v, ok := result.RawClaims["name"].(string); ok {
+			name = v
+		}
+	}
+
+	if email == "" {
+		// last resort: use the subject as a pseudo-email
+		s.Logger.Warnw("oidc provider did not return an email address, using sub", "sub", sub)
+		email = sub
+	}
+	if name == "" {
+		name = strings.Split(email, "@")[0]
+	}
+
+	userID, err := s.UserService.CreateFromSSO(ctx, name, email, sub)
+	if err != nil {
+		return nil, errs.Wrap(err)
+	}
+	if userID == nil {
+		return nil, errs.Wrap(errors.New("user ID is unexpectedly nil after CreateFromSSO"))
+	}
+
+	user, err := s.UserService.GetByIDWithoutAuth(ctx, userID)
+	if err != nil {
+		s.Logger.Errorw("failed to get OIDC user after create", "error", err)
+		return nil, errs.Wrap(err)
+	}
+
+	session, err := s.SessionService.Create(ctx, user, clientIP)
+	if err != nil {
+		s.Logger.Errorw("failed to create session from OIDC login", "error", err)
+		return nil, errs.Wrap(err)
+	}
+	return session, nil
+}
+
+// CleanupExpiredSSOStates removes expired PKCE/state records from the store.
+// It is safe to call at any time; errors are logged but not propagated.
+func (s *SSO) CleanupExpiredSSOStates(ctx context.Context) {
+	if err := s.SSOStateRepo.DeleteExpired(ctx); err != nil {
+		s.Logger.Warnw("failed to clean up expired sso states", "error", err)
+	}
+}
diff --git a/backend/service/user.go b/backend/service/user.go
index 11e9d0b..b41aab4 100644
--- a/backend/service/user.go
+++ b/backend/service/user.go
@@ -39,6 +39,8 @@ type User struct {
 	CompanyRepository *repository.Company
 	PasswordVerifier  *password.Argon2Verifier
 	PasswordHasher    *password.Argon2Hasher
+	// OptionRepository is used to check the SSO-only policy on login.
+	OptionRepository *repository.Option
 }
 
 // Create creates a new user
@@ -835,6 +837,19 @@ func (u *User) AuthenticateUsernameWithPassword(
 	ae := NewAuditEvent("User.AuthenticateUsernameWithPassword", nil)
 	ae.IP = ip
 	ae.Details["username"] = username
+
+	// enforce SSO-only policy: reject local logins when the feature is active
+	if u.OptionRepository != nil {
+		opt, optErr := u.OptionRepository.GetByKey(ctx, data.OptionKeyAdminSSOLogin)
+		if optErr == nil && opt != nil {
+			ssoOpt, parseErr := model.NewSSOOptionFromJSON([]byte(opt.Value.String()))
+			if parseErr == nil && ssoOpt.Enabled && ssoOpt.SSOOnly {
+				u.Logger.Debugw("local login rejected: sso-only mode is active", "username", username)
+				return nil, errs.ErrAuthenticationFailed
+			}
+		}
+	}
+
 	// check the entities are valid before doing anything
 	usernameEntity, err := vo.NewUsername(username)
 	if err != nil {
diff --git a/backend/sso/oidc.go b/backend/sso/oidc.go
new file mode 100644
index 0000000..e9c6fe0
--- /dev/null
+++ b/backend/sso/oidc.go
@@ -0,0 +1,293 @@
+package sso
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"strings"
+	"time"
+
+	gooidc "github.com/coreos/go-oidc/v3/oidc"
+	"golang.org/x/oauth2"
+)
+
+// OIDCClient wraps the go-oidc provider and the oauth2 config so that
+// the service layer has a single, stable type to work with.
+type OIDCClient struct {
+	provider *gooidc.Provider
+	oauth2   oauth2.Config
+	verifier *gooidc.IDTokenVerifier
+}
+
+// NewOIDCClient discovers the provider metadata from issuerURL and constructs
+// an OIDCClient ready for use.  The discovery document is fetched during
+// construction so any network or configuration error is surfaced early.
+func NewOIDCClient(
+	ctx context.Context,
+	issuerURL string,
+	clientID string,
+	clientSecret string,
+	redirectURL string,
+	scopes []string,
+) (*OIDCClient, error) {
+	if issuerURL == "" {
+		return nil, fmt.Errorf("issuerURL must not be empty")
+	}
+	if clientID == "" {
+		return nil, fmt.Errorf("clientID must not be empty")
+	}
+	if redirectURL == "" {
+		return nil, fmt.Errorf("redirectURL must not be empty")
+	}
+
+	provider, err := gooidc.NewProvider(ctx, issuerURL)
+	if err != nil {
+		return nil, fmt.Errorf("oidc provider discovery failed for %q: %w", issuerURL, err)
+	}
+
+	// always include openid; callers may add profile and email
+	merged := mergeScopes([]string{gooidc.ScopeOpenID}, scopes)
+
+	cfg := oauth2.Config{
+		ClientID:     clientID,
+		ClientSecret: clientSecret,
+		RedirectURL:  redirectURL,
+		Endpoint:     provider.Endpoint(),
+		Scopes:       merged,
+	}
+
+	verifier := provider.Verifier(&gooidc.Config{
+		ClientID: clientID,
+	})
+
+	return &OIDCClient{
+		provider: provider,
+		oauth2:   cfg,
+		verifier: verifier,
+	}, nil
+}
+
+// AuthCodeURL returns the authorization endpoint URL with the supplied state,
+// nonce, PKCE challenge and optional ACR values.
+func (c *OIDCClient) AuthCodeURL(
+	state string,
+	nonce string,
+	codeChallenge string,
+	acrValues string,
+) string {
+	opts := []oauth2.AuthCodeOption{
+		gooidc.Nonce(nonce),
+		oauth2.SetAuthURLParam("code_challenge", codeChallenge),
+		oauth2.SetAuthURLParam("code_challenge_method", "S256"),
+	}
+	if acrValues != "" {
+		opts = append(opts, oauth2.SetAuthURLParam("acr_values", acrValues))
+	}
+	return c.oauth2.AuthCodeURL(state, opts...)
+}
+
+// OIDCTokenResult is returned from ExchangeCode.
+type OIDCTokenResult struct {
+	// AccessToken is the raw access token from the provider.
+	AccessToken string
+	// IDToken is the verified, parsed id_token.
+	IDToken *gooidc.IDToken
+	// RawClaims are all claims extracted from the id_token.
+	RawClaims map[string]any
+}
+
+// ExchangeCode exchanges the authorisation code for tokens, verifies the
+// id_token signature and nonce, and returns the result.
+func (c *OIDCClient) ExchangeCode(
+	ctx context.Context,
+	code string,
+	codeVerifier string,
+	expectedNonce string,
+) (*OIDCTokenResult, error) {
+	token, err := c.oauth2.Exchange(
+		ctx,
+		code,
+		oauth2.SetAuthURLParam("code_verifier", codeVerifier),
+	)
+	if err != nil {
+		return nil, fmt.Errorf("token exchange failed: %w", err)
+	}
+
+	rawIDToken, ok := token.Extra("id_token").(string)
+	if !ok {
+		return nil, fmt.Errorf("provider did not return an id_token")
+	}
+
+	idToken, err := c.verifier.Verify(ctx, rawIDToken)
+	if err != nil {
+		return nil, fmt.Errorf("id_token verification failed: %w", err)
+	}
+
+	if idToken.Nonce != expectedNonce {
+		return nil, fmt.Errorf("id_token nonce mismatch: got %q, want %q", idToken.Nonce, expectedNonce)
+	}
+
+	var claims map[string]any
+	if err := idToken.Claims(&claims); err != nil {
+		return nil, fmt.Errorf("failed to extract id_token claims: %w", err)
+	}
+
+	return &OIDCTokenResult{
+		AccessToken: token.AccessToken,
+		IDToken:     idToken,
+		RawClaims:   claims,
+	}, nil
+}
+
+// UserInfoEmail fetches the userinfo endpoint and returns the sub, email and
+// name claims as plain strings.  The access token from ExchangeCode is used.
+func (c *OIDCClient) UserInfoEmail(
+	ctx context.Context,
+	accessToken string,
+) (sub, email, name string, err error) {
+	src := oauth2.StaticTokenSource(&oauth2.Token{AccessToken: accessToken})
+	info, infoErr := c.provider.UserInfo(ctx, src)
+	if infoErr != nil {
+		return "", "", "", fmt.Errorf("userinfo request failed: %w", infoErr)
+	}
+
+	sub = info.Subject
+
+	var extra struct {
+		Email string `json:"email"`
+		Name  string `json:"name"`
+	}
+	if claimErr := info.Claims(&extra); claimErr != nil {
+		// non-fatal: we still have the subject
+		_ = claimErr
+	}
+	email = extra.Email
+	name = extra.Name
+	return sub, email, name, nil
+}
+
+// CheckRoleClaim inspects rawClaims for the claim identified by claimPath and
+// checks whether requiredValue is present.
+//
+// claimPath supports a single dot-separated path into nested objects, e.g.
+// "realm_access.roles" will look up claims["realm_access"]["roles"].  The
+// leaf value may be a string, a []interface{} (JSON array of strings), or a
+// JSON-encoded array embedded inside another claim value.
+//
+// Returns true when the required value is found, false otherwise.
+func CheckRoleClaim(
+	rawClaims map[string]any,
+	claimPath string,
+	requiredValue string,
+) bool {
+	if claimPath == "" || requiredValue == "" {
+		return true // gating disabled
+	}
+
+	parts := strings.SplitN(claimPath, ".", 2)
+	top, ok := rawClaims[parts[0]]
+	if !ok {
+		return false
+	}
+
+	// descend one level for dotted paths, e.g. "realm_access.roles"
+	var leaf any = top
+	if len(parts) == 2 {
+		nested, isMap := top.(map[string]any)
+		if !isMap {
+			return false
+		}
+		leaf, ok = nested[parts[1]]
+		if !ok {
+			return false
+		}
+	}
+
+	return containsValue(leaf, requiredValue)
+}
+
+// containsValue returns true when v equals requiredValue or v is a slice
+// that contains requiredValue.
+func containsValue(v any, requiredValue string) bool {
+	switch typed := v.(type) {
+	case string:
+		return typed == requiredValue
+	case []any:
+		for _, item := range typed {
+			if s, ok := item.(string); ok && s == requiredValue {
+				return true
+			}
+		}
+	case []string:
+		for _, s := range typed {
+			if s == requiredValue {
+				return true
+			}
+		}
+	default:
+		// attempt JSON-encoded array stored as a plain string
+		if raw, ok := v.(string); ok {
+			var arr []string
+			if err := json.Unmarshal([]byte(raw), &arr); err == nil {
+				for _, s := range arr {
+					if s == requiredValue {
+						return true
+					}
+				}
+			}
+		}
+	}
+	return false
+}
+
+// GeneratePKCEPair generates a cryptographically random code_verifier and
+// derives the S256 code_challenge from it.
+//
+// The verifier is a 64-byte URL-safe base64-encoded random value (no padding).
+// The challenge is the base64url encoding (no padding) of the SHA-256 digest
+// of the verifier as required by RFC 7636 §4.2.
+func GeneratePKCEPair() (verifier string, challenge string, err error) {
+	b, err := generateRandomBytes(64)
+	if err != nil {
+		return "", "", fmt.Errorf("failed to generate PKCE verifier bytes: %w", err)
+	}
+	verifier = base64.RawURLEncoding.EncodeToString(b)
+	sum := sha256.Sum256([]byte(verifier))
+	challenge = base64.RawURLEncoding.EncodeToString(sum[:])
+	return verifier, challenge, nil
+}
+
+// GenerateStateToken generates a cryptographically random URL-safe state token
+// suitable for use as the OAuth2 'state' and OIDC 'nonce' parameters.
+func GenerateStateToken() (string, error) {
+	b, err := generateRandomBytes(32)
+	if err != nil {
+		return "", fmt.Errorf("failed to generate state token: %w", err)
+	}
+	return base64.RawURLEncoding.EncodeToString(b), nil
+}
+
+// SSOStateExpiry is how long an SSO state token remains valid.
+const SSOStateExpiry = 10 * time.Minute
+
+// mergeScopes returns a deduplicated slice with base prepended then extras
+// appended, preserving order.
+func mergeScopes(base, extra []string) []string {
+	seen := make(map[string]struct{}, len(base)+len(extra))
+	out := make([]string, 0, len(base)+len(extra))
+	for _, s := range base {
+		if _, ok := seen[s]; !ok {
+			seen[s] = struct{}{}
+			out = append(out, s)
+		}
+	}
+	for _, s := range extra {
+		if _, ok := seen[s]; !ok {
+			seen[s] = struct{}{}
+			out = append(out, s)
+		}
+	}
+	return out
+}
diff --git a/backend/sso/random.go b/backend/sso/random.go
new file mode 100644
index 0000000..f09000d
--- /dev/null
+++ b/backend/sso/random.go
@@ -0,0 +1,15 @@
+package sso
+
+import (
+	"crypto/rand"
+	"fmt"
+)
+
+// generateRandomBytes generates n cryptographically random bytes.
+func generateRandomBytes(n int) ([]byte, error) {
+	b := make([]byte, n)
+	if _, err := rand.Read(b); err != nil {
+		return nil, fmt.Errorf("failed to read random bytes: %w", err)
+	}
+	return b, nil
+}
diff --git a/backend/vendor/modules.txt b/backend/vendor/modules.txt
index a03a15a..33876e8 100644
--- a/backend/vendor/modules.txt
+++ b/backend/vendor/modules.txt
@@ -122,6 +122,9 @@ github.com/cloudwego/base64x
 ## explicit; go 1.16
 github.com/cloudwego/iasm/expr
 github.com/cloudwego/iasm/x86_64
+# github.com/coreos/go-oidc/v3 v3.17.0
+## explicit; go 1.24.0
+github.com/coreos/go-oidc/v3/oidc
 # github.com/davecgh/go-spew v1.1.1
 ## explicit
 github.com/davecgh/go-spew/spew
@@ -235,6 +238,11 @@ github.com/gin-gonic/gin/render
 # github.com/go-errors/errors v1.5.1
 ## explicit; go 1.14
 github.com/go-errors/errors
+# github.com/go-jose/go-jose/v4 v4.1.3
+## explicit; go 1.24.0
+github.com/go-jose/go-jose/v4
+github.com/go-jose/go-jose/v4/cipher
+github.com/go-jose/go-jose/v4/json
 # github.com/go-playground/locales v0.14.1
 ## explicit; go 1.17
 github.com/go-playground/locales
@@ -529,6 +537,10 @@ golang.org/x/net/ipv4
 golang.org/x/net/ipv6
 golang.org/x/net/proxy
 golang.org/x/net/publicsuffix
+# golang.org/x/oauth2 v0.28.0
+## explicit; go 1.23.0
+golang.org/x/oauth2
+golang.org/x/oauth2/internal
 # golang.org/x/sync v0.18.0
 ## explicit; go 1.24.0
 golang.org/x/sync/errgroup