This PR was merged into the 2.3.x-dev branch.

Discussion
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Allow defining users provider as a service ID

Replaces #1217.
Closes #1216.

Commits
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81961b82 Fix typo in security docs
4c0cd2ba Update password in tests
cb44f3f0 Update code style - use short array syntax
bac2c455 add test and documentation for using a service id string instead of a closure
dc7572ef allow using a service name for the users config in firewall