Basic auth (username and password) broken after upgrade to 17.5.x

On our self-managed CE instance, we have upgraded from version 17.3.6 to version 17.5.1.

Since this upgrade, we could no longer authenticate with basic auth (username and password): git clone or docker login. Local and real users (external authentication = LDAP) were affected.

Installing patch 17.5.5 solved the problem for local users, but not for real users (external authentication).

• Local user = user created manually in gitlab, therefore not present in LDAP
• Real users = user present in our LDAP

We use the same crendentials for git and docker login !

For sign-in configuration, here's what we have :

• Allow password authentication for the web interface => disabled
• Allow password authentication for Git via HTTP(S) => enabled
• Disable password authentication for users with an SSO identity => disabled
• Two-factor authentication => disabled
• Enforce Two-Factor authentication for administrator users => disabled

gitlab-rake gitlab:ldap:check => success

Checking LDAP ...

LDAP: ... Server: ldapmain
LDAP authentication... Success

It seems that during authentication, there is no call to our LDAP 😞