Add missing unit test for token middleware

[benkroeger]

as discussed in #2108

[bajtos]

@benkroeger It's better to open a pull request directly, there is no need to create short-lived placeholder issues like this one.

[benkroeger]

just following the git-flow concept here. And I need an issue in order to name my branch correctly.

[benkroeger]

landed in 2.29.1