Could you please bring this pull request up to date with master? Alternatively you can allow me to update your branch, then I can do it myself via GitHub most of the time.

I did a rebase on the current master.

@sebastian-meyer we have to remove the temporary file in TokenRepositoryTest.php:46, but according to Codacy
The use of function shell_exec() is forbidden and
The use of function unlink() is discouraged.
Do you see any other way to remove the file or should I use unlink as it is "just" discouraged?
(I will fix the other Codacy issues.)

Yes, please revert this back to unlink(), since this is more portable than shell_exec() (which only works on UNIX and is disabled on many shared hosting services for security reasons). I'll then look into which rule actually discourages using unlink() and how to make an exception in this case.