feat(oidc): provide reason of autolink failure

src/application/services/auth_application_service.rs

@@ -56,6 +56,14 @@ pub enum OidcCallbackResult {
     /// `/profile?link_error=<reason>` redirect. See
     /// docs/plan/oidc-account-linking.md § Safety checks.
     LinkRefused { reason: &'static str },
+    /// Auto-link decision refused during the OIDC LOGIN callback path
+    /// (existing local user matched by email but the decision tree
+    /// rejected). `reason` is one of `auto_link_disabled`,
+    /// `auto_link_email_not_verified`, `already_linked_elsewhere`;
+    /// the handler maps each to a distinct CamelCase `error_type`
+    /// on the 409 response so the login page can switch on it.
+    /// See docs/plan/oidc-account-linking.md § Auto-link.
+    AutoLinkRefused { reason: &'static str },
 }
 
 /// Outcome of a successful magic-link redemption. The auth tokens are
@@ -3877,14 +3885,15 @@ impl AuthApplicationService {
                             reason = reason,
                             "🔗 auto-link refused",
                         );
-                        return Err(DomainError::new(
-                            ErrorKind::AlreadyExists,
-                            "OIDC",
-                            format!(
-                                "A user with email '{}' already exists. Contact admin to link your OIDC identity.",
-                                oidc_email
-                            ),
-                        ));
+                        // Ok(AutoLinkRefused) rather than Err(AlreadyExists)
+                        // so the handler can map each reason to a distinct
+                        // stable CamelCase error_type (AutoLinkDisabled /
+                        // AutoLinkEmailNotVerified / AutoLinkAlreadyLinked-
+                        // Elsewhere). Bubbling as a generic AlreadyExists
+                        // would collapse all three reasons into "Already
+                        // Exists" on the wire and leave the SPA without a
+                        // switch arm for user-facing copy.
+                        return Ok(OidcCallbackResult::AutoLinkRefused { reason });
                     }
 
                     // All checks passed — commit the auto-link, re-fetch

src/interfaces/api/handlers/auth_handler.rs

@@ -1582,6 +1582,27 @@ pub async fn oidc_callback(
             );
             Ok(Redirect::temporary(&redirect_url).into_response())
         }
+        // Map each auto-link refusal reason to a distinct stable
+        // CamelCase `error_type`. The SPA switches on this to render
+        // targeted copy (contact-admin vs. verify-email-at-IdP vs.
+        // already-linked-elsewhere) rather than a generic error toast.
+        // Status stays 409 (CONFLICT) — semantically an existing user
+        // blocks the auto-provision path.
+        OidcCallbackResult::AutoLinkRefused { reason } => {
+            let error_type = match reason {
+                "auto_link_disabled" => "AutoLinkDisabled",
+                "auto_link_email_not_verified" => "AutoLinkEmailNotVerified",
+                "already_linked_elsewhere" => "AutoLinkAlreadyLinkedElsewhere",
+                _ => "AutoLinkRefused",
+            };
+            Err(AppError::new(
+                StatusCode::CONFLICT,
+                "OIDC login blocked — a local account with this email already exists. \
+                 Contact your administrator, or sign in with your existing credentials \
+                 and connect SSO from your profile.",
+                error_type,
+            ))
+        }
     }
 }
 

tests/oidc/link_unlink.hurl

@@ -40,8 +40,9 @@
 #        (iss, sub) miss but email matches admin, so it auto-
 #        links + logs admin in.
 #     2. Auto-link refused — email_verified=false. Callback
-#        returns HTTP 409 with error_type "Already Exists" (the
-#        "contact admin to link your OIDC identity" refusal).
+#        returns HTTP 409 with error_type "AutoLinkEmailNotVerified"
+#        (one of three distinct auto-link refusal error_types —
+#        see auth_handler.rs AutoLinkRefused arm).
 #
 #   [OIDC-only user]
 #    10. `oidc_user` unlink refused (would lock them out) with
@@ -491,12 +492,10 @@ HTTP 200
 # "contact admin to link your OIDC identity" text that surfaces
 # in the SPA login form's error toast.
 #
-# NOTE: `error_type` here is "Already Exists" (with a space)
-# because it comes from `ErrorKind::as_str()`, not from a
-# handler-set stable key. The auto-link refusal branch is
-# reusing the generic AlreadyExists mapping — a follow-up
-# could give it a dedicated `error_type` like
-# `AutoLinkEmailNotVerified` for the SPA to switch on.
+# The handler maps each auto-link refusal reason to a distinct
+# CamelCase error_type — AutoLinkDisabled /
+# AutoLinkEmailNotVerified / AutoLinkAlreadyLinkedElsewhere —
+# so the SPA can render targeted copy per refusal reason.
 # ═════════════════════════════════════════════════════════════
 
 
@@ -522,7 +521,10 @@ location-trusted: true
 
 HTTP 409
 [Asserts]
-jsonpath "$.error_type" == "Already Exists"
+# Distinct CamelCase key per auto-link refusal reason — the SPA
+# switches on this to render "verify your email at the IdP" copy
+# rather than the generic contact-admin fallback.
+jsonpath "$.error_type" == "AutoLinkEmailNotVerified"
 
 
 # Belt-and-braces invariant: admin's row is still un-linked