feat(dotnet-sdk): configurable client credentials token url

[alex-zyl]

Description

Makes token endpoint configurable.

References

#238

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[linux-foundation-easycla]

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• ✅ login: alex-zyl / name: Alex Zyl (a203e06)

[rhamzeh]

Thanks for the PR @alex-zyl - sorry it's taking a bit longer to review, we're clearing through a backlog of .NET related changes and PRs and hopefully this week or early next week we can get this reviewed and merged

[alex-zyl]

No worries, @rhamzeh

Luckily the issue with hardcoded token endpoint subpath can be workedaround by providing own instance of http client where we can overwrite request url

[jamp-scp28]

Hey @alex-zyl, just an opinion; but seems to me we're not addressing the root issue, a better solution should involve Discovery, it might require some work though.

On the other hand, if a workaround is to be provided, I think the PR might introduce edge cases and breaking changes on clients relying already on that PathTemplate; just and idea but why just not adding a new variable to the ClientConfiguration.Credentials and use it for the PathTemplate if not null?