🛂(backend) oidc userinfo endpoint json format

The userinfo endpoint can return 2 content types:
- application/json
- application/jwt

Gitlab oidc returns a json object, while
Agent Connect oidc returns a jwt token.
We are adapting the authentication to handle both cases.

src/backend/core/authentication/backends.py

@@ -45,7 +45,17 @@ class OIDCAuthenticationBackend(MozillaOIDCAuthenticationBackend):
             proxies=self.get_settings("OIDC_PROXY", None),
         )
         user_response.raise_for_status()
-        userinfo = self.verify_token(user_response.text)
+
+        try:
+            userinfo = user_response.json()
+        except ValueError:
+            try:
+                userinfo = self.verify_token(user_response.text)
+            except Exception as e:
+                raise SuspiciousOperation(
+                    _("Invalid response format or token verification failed")
+                ) from e
+
         return userinfo
 
     def get_or_create_user(self, access_token, id_token, payload):