feat: support custom path in apiTokenIssuer

[marcoquotech]

Description

This PR modifies the refreshAccessToken method to conditionally append the /oauth/token endpoint to the apiTokenIssuer only when the apiTokenIssuer does not include its own path. This ensures that the URL is correctly formed whether the issuer contains a custom path or is just a domain.

References

Closes #141

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
• 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]

• ✅login: marcoquotech / (bb6d84c)

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[rhamzeh]

Thanks @marcoquotech!

Instead of accepting this, would you mind keeping this in tandem with the support we have in other SDKs.

You can reference this ticket for the details: openfga/sdk-generator#238

Change the apiTokenIssuer field in the configuration to accept a full URL.
So:

ApiTokenIssuer	Endpoint SDK will hit
issuer.fga.example	https://issuer.fga.example/oauth/token
https://issuer.fga.example	https://issuer.fga.example/oauth/token
https://issuer.fga.example:8080	https://issuer.fga.example:8080/oauth/token
issuer.fga.example/some_endpoint	https://issuer.fga.example/some_endpoint
https://issuer.fga.example/some_endpoint	https://issuer.fga.example/some_endpoint
https://issuer.fga.example:8080/some_endpoint	https://issuer.fga.example:8080/some_endpoint

We would also like to see tests to ensure that this is working as expected, see the tests in the Go SDK for example:

https://github.com/openfga/go-sdk/blob/main/api_open_fga_test.go#L277-L319