Mastodon clients can sign in: OAuth with a persona per token

OpenIddict 7.7 (MongoDB stores, keys kept in Mongo so tokens survive
restarts) serves /oauth/authorize, /oauth/token, /oauth/revoke and the
discovery documents, including /.well-known/oauth-authorization-server:
- authorization code (PKCE optional) and client credentials, Mastodon's
  scopes including the granular ones, non-expiring reference tokens,
  `created_at` in the token response, and the urn:ietf:wg:oauth:2.0:oob
  page that shows the code;
- /oauth/login signs the private login into a fifteen-minute cookie that
  only /oauth sees (rate limited, antiforgery-protected); /oauth/authorize
  then asks which persona the application acts as. The token's subject
  is that persona's id and nothing else; no root id reaches a token, an
  authorization or a log line;
- the token exchange refuses a persona whose login is banned or deleted,
  and every API request checks the same.

/api/v1/apps registers applications dynamically, /api/v1/apps/
verify_credentials, /api/v1/instance (v1 and v2, "4.2.0 (compatible;
PrivaPub)") and verify_credentials answer in Mastodon's shapes: snake_case
with explicit nulls, Rails-style parameters from query, form or JSON,
{"error": ...} on failure, Link paging. CORS exposes Link.

/api goes to OpenIddict validation and everything else to the existing
JWT; the JWT failure handler no longer sends the exception and stack trace
to the client.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

PrivaPub/Middleware/SocialPubConfigurations.cs

@@ -1,6 +1,8 @@
 using Microsoft.AspNetCore.Authentication.JwtBearer;
 using Microsoft.AspNetCore.ResponseCompression;
 
+using OpenIddict.Validation.AspNetCore;
+
 using PrivaPub.ClientModels;
 using PrivaPub.Extensions;
 using PrivaPub.Models;
@@ -27,6 +29,8 @@ namespace PrivaPub.Middleware
 {
 	public static class PrivaPubConfigurations
 	{
+		const string SchemeSelector = "PrivaPub";
+
 		public static IServiceCollection PrivaPubAppSettingsConfiguration(this IServiceCollection service, IConfiguration configuration)
 		{
 			return service
@@ -89,10 +93,14 @@ namespace PrivaPub.Middleware
 				})
 				.AddAuthentication(options =>
 				{
-					options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
-					options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
-					options.DefaultScheme = JwtBearerDefaults.AuthenticationScheme;
+					options.DefaultAuthenticateScheme = SchemeSelector;
+					options.DefaultChallengeScheme = SchemeSelector;
+					options.DefaultScheme = SchemeSelector;
 				})
+				.AddPolicyScheme(SchemeSelector, SchemeSelector, options => options.ForwardDefaultSelector = context =>
+					context.Request.Path.StartsWithSegments("/api")
+						? OpenIddictValidationAspNetCoreDefaults.AuthenticationScheme
+						: JwtBearerDefaults.AuthenticationScheme)
 				.AddPrivaPubAuth(configuration)
 				.Services
 				.AddSingleton<AuthTokenManager>()
@@ -179,7 +187,7 @@ namespace PrivaPub.Middleware
 					configure.AllowAnyMethod()
 						.AllowAnyHeader()
 						.AllowAnyOrigin()
-						.AllowAnyMethod()
+						.WithExposedHeaders("Link", "X-RateLimit-Remaining", "X-RateLimit-Reset")
 						.DisallowCredentials();
 				});
 			});