## Summary
In this pull request we're adding support for OIDC allowed groups in the
OSS version as part of work for
https://github.com/coder/coder/issues/17027.
### Changes
- Restored support for parsing group allow list in OSS code
### Testing
- Added tests for OSS code
- Tested allowed/prohibited group OIDC flows in premium and OSS
Related to https://github.com/coder/coder/issues/15109.
Running postgres tests used to create a new postgres docker container
every time. I believe the slow down might've been caused by that and was
misattributed to postgres performance.
```
coder@main ~/coder ((0e90ac29))> DB=ci gotestsum --packages="./coderd/idpsync" -- -count=1
✓ coderd/idpsync (1.471s)
DONE 91 tests in 4.766s
```
The experimental functions in `golang.org/x/exp/slices` are now
available in the standard library since Go 1.21.
Reference: https://go.dev/doc/go1.21#slices
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>
Rafael Rodriguez