zulip/templates/zerver/authentication_backends/gitlab-error.html

<p>
    You are attempting to use the <strong>GitLab auth backend</strong>, but it
    is not properly configured. To configure, please check the following:
</p>
<ul>
    <li>
        You have added
        <code>{{ root_domain_url }}/complete/gitlab/</code> as the callback URL
        in the OAuth application in GitLab. You can register OAuth apps at
        <a href="https://gitlab.com/profile/applications">GitLab
        applications</a>.
    </li>
    <li>
        You have set <code>{{ client_id_key_name }}</code> in
        <code>{{ settings_path }}</code> and
        <code>social_auth_gitlab_secret</code> in
        <code>{{ secrets_path }}</code> with the values from your OAuth
        application.
    </li>
    <li>
        Navigate back to the login page and attempt the GitLab auth flow again.
    </li>
</ul>