Lost access to gitlab server

After a fresh install of gitlab-ce on an ubuntu server, everything was up and running (I am a gitlab newbie).

I wanted that only users with a SSH key could access to the gitlab server. But I misunderstood gitlab instructions for securing the server, and did the following sequence of operations:

  1. added a SSH key
  2. removed HTTP access from gitlab (by disabling password access checkbox in gitlab settings; )
  3. logged out

Now, I realize that it was a terrible blunder as I cannot sign in anymore to the gitlab server. There still exists a signin page (…/sign_in#js-signin-settings) but the signin button is disabled.

Is there any way I can recover the server from this situation ?

It’s unclear to me what you have done, but you can try to enable HTTP access through the API. Look at
https://docs.gitlab.com/ee/api/settings.html