Log warning when no uid was found for user

[PVince81]

In some incomplete setups (like mine) it can happen that the uid
attribute of users is missing.

To be able to find out that something is wrong, a debug message is now
logged when it has not been found.

To test:

1. Create a user but omit the "uid" attribute (I had "cn" set and did not know I had to set "uid" as well)
2. Add that user in a LDAP group and make sure the group memberships are visible in OC
3. Go to the admin page
4. Exclude the user's group from sharing
5. Refresh the page

Before this PR: no warnings message
After this PR: a warning message appears in the log (debug level)

Note that "exclude user group from sharing" does not work when uid is not set, but this is not ownCloud's fault.

@blizzz

[PVince81]

@blizzz can you confirm that it is expected that every user has a "uid" attribute and no fallback to "cn" is required ?

[blizzz]

Depends on LDAP server, uid is most common, samaccoutname it is on AD.

In this context, AD will not fall into this path and i did find an LDAP server yet which does not incorporate uid attribute. So this is pretty safe to assume here, also because it is specified in an RFC for login uses.

[PVince81]

Ok, good to know. Then this PR will help people like me who incorrectly setup their LDAP users.

[blizzz]

Yes. 👍

[ghost]

🚀 Test PASSed. 🚀
Refer to this link for build results (access rights to CI server needed):
https://ci.owncloud.org//job/pull-request-analyser-ng/183/:rocket: Test PASSed. 🚀

[scrutinizer-notifier]

The inspection completed: 1 new issues

[LukasReschke]

👍

[PVince81]

@karlitschek backport to stable7 ? can be useful when troubleshooting LDAP issues

[karlitschek]

Yes. Backport

[PVince81]

stable7: b297ddf