identity: simplify user sign up

Streetwriters.Common/Models/SignupResponse.cs

@@ -0,0 +1,30 @@
+using System.Collections.Generic;
+using System.Linq;
+using System.Text.Json.Serialization;
+using Streetwriters.Common.Models;
+
+namespace Streetwriters.Common.Models
+{
+    public class SignupResponse
+    {
+        [JsonPropertyName("access_token")]
+        public string AccessToken { get; set; }
+        [JsonPropertyName("expires_in")]
+        public int AccessTokenLifetime { get; set; }
+        [JsonPropertyName("refresh_token")]
+        public string RefreshToken { get; set; }
+        [JsonPropertyName("scope")]
+        public string Scope { get; set; }
+        [JsonPropertyName("user_id")]
+        public string UserId { get; set; }
+        public string[]? Errors { get; set; }
+
+        public static SignupResponse Error(IEnumerable<string> errors)
+        {
+            return new SignupResponse
+            {
+                Errors = [.. errors]
+            };
+        }
+    }
+}