What do 502/503 mean in the context of Gitlab SSO?

Troubleshooting
3

Thanks for the reply @jwilander.

I guess I should clarify what I mean by it “working” from curl. Since it seems these APIs communicate by passing POST vars back and forth, I wasn’t actually trying to replicate the traffic. I only made very basic GET requests with no parameters each direction and verified that the reply I got (error notwithstanding) was generated by the correct service. In other words the endpoints are reachable.

Here is the relevant part of my config.json file (obviously with the private data replaced with asterisks):

"SSOSettings": {
    "gitlab": {
        "Allow": true,
        "Secret" : "a**************************************************************2",
        "Id": "8**************************************************************9",
        "Scope": "",
        "AuthEndpoint": "http://127.0.0.1:8080/oauth/authorize",
        "TokenEndpoint": "http://127.0.0.1:8080/oauth/token",
        "UserApiEndpoint": "http://127.0.0.1:8080/api/v3/user"
    }
},

And here is the corresponding application setup in Gitlab:

My Apache config for the proxy also happens to be posted in this other topic.

Also for good measure here is what the Firefox Network console turns up if I load the page and submit two consecutive requests.

Note that is in fact the public URL of the Mattermost instance (proxied through Apache from its localhost port) and the matching Gitlab instance is where you might expect on the same host and proxied the same way. As this error occurs before a user is ever authenticated in Gitlab you should be able to replicate the error yourself.