Description:

After upgrading Rocket.Chat to version 4.1.0, OAuth no longer works with GitLab.
You get an undefined error after successful login to our self-managed GitLab instance.

Steps to reproduce:

1. Upgrade Rocket.Chat to version 4.1.0
2. Click login with GitLab OAuth
3. Login into GitLab instance
4. Undefined error triggered -> Login failed

Server Setup Information:

• Version of Rocket.Chat Server: 4.1.0
• Operating System: Debian
• Deployment Method: Docker
• Number of Running Instances: 1
• DB Replicaset Oplog: yes
• NodeJS Version: v12.22.1
• MongoDB Version: 4.2.17 / wiredTiger

Client Setup Information

• Desktop App or Browser Version: Chrome / Safari
• Operating System: Windows / MacOS / iOS / iPadOS

Additional context

The GitLab-URL is set to our self hosted GitLab instance.
The problem is present since version 4.1.0

Relevant logs:

{"level":50,"time":"2021-11-02T19:42:55.310Z","pid":9,"hostname":"XXX","name":"System","msg":"Exception while invoking method login 'Failed to complete OAuth handshake with gitlab at https://gitlab.com/oauth/token. failed [401] {\"error\":\"invalid_client\",\"error_description\":\"Client authentication failed due to unknown client, no client authentication included, or unsupported authentication method.\"}'"}