fix(auth): do not auto-reactivate disabled users on OAuth2 callback (#38009) (#38183)

Backport #38009

The OAuth2 sign-in callback unconditionally set IsActive=true on the
local user row whenever the IdP authenticated them, silently undoing an
administrator's "Disable Account" action and granting the user a fresh
session in the same response. Treat the local IsActive flag as an
authoritative admin override: inactive users get a session and are
routed through the existing activate / prohibit-login pages by
verifyAuthWithOptions, matching the local-credentials sign-in path.

Adds an integration regression test that disables a linked local user
and asserts the row stays IsActive=false after a full OIDC callback.

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/auth/oauth.go

@@ -368,9 +368,21 @@ func handleOAuth2SignIn(ctx *context.Context, authSource *auth.Source, u *user_m
 
 	opts := &user_service.UpdateOptions{}
 
-	// Reactivate user if they are deactivated
+	// HINT: OAUTH-AUTO-SYNC-USER-ACTIVATION: see services/auth/source/oauth2/source_sync.go
+	// Reactivate user only if they were disabled by the OAuth2 auto sync cron (invalid_grant),
+	// which clears AccessToken/RefreshToken/ExpiresAt on the ExternalLoginUser row
+	// An admin-disabled user has no such signature, so we leave IsActive alone
+	// and let verifyAuthWithOptions route them through the prohibit-login / activate page.
 	if !u.IsActive {
-		opts.IsActive = optional.Some(true)
+		extLogin, hasExt, err := user_model.GetExternalLogin(ctx, authSource.ID, gothUser.UserID)
+		if err != nil {
+			ctx.ServerError("GetExternalLogin", err)
+			return
+		}
+		isDisabledByAutoSync := hasExt && extLogin.RefreshToken == ""
+		if isDisabledByAutoSync {
+			opts.IsActive = optional.Some(true)
+		}
 	}
 
 	// Update GroupClaims