Issue-26 - Accept Explicit Project Id.

[Sydney-o9]

Context

When Firebase and infrastructure run in separate GCP projects, GOOGLE_CLOUD_PROJECT is already taken by the infrastructure project.

This pull request adds a constructor as reported in Issue 26 that accepts the Firebase project ID directly, bypassing env var and credential header resolution adequately.

There are no breaking changes. 2 breaking changes have been reported and fixed.

Changes

• lib/src/lib.rs — new App::live_with_project_id(project_id: &str) on App<AccessTokenCredentials>
• README.md — usage example and motivation for the new constructor
• examples/explicit_project_id/ — runnable example

[Sydney-o9]

@expl All formatting / linting / tests are passing and the workflow will now pass if you run it.

[expl]

Thank you for your PR and sorry for not replying promptly.

Some feedback:

1. A full example just to demonstrate a new constructor is probably not required.
2. Due to an oversight in my implementation, this change breaks the id_token_verifier() and cookie_token_verifier() implementation on the same impl block, just assigning project_id to self.project_id.clone() is sufficient and would not break with your change, do you mind including this in your PR?

[Sydney-o9]

Thank you for your PR and sorry for not replying promptly.

@expl 👍

1. A full example just to demonstrate a new constructor is probably not required.

Addressed in 09ca552

2. Due to an oversight in my implementation, this change breaks the id_token_verifier() and cookie_token_verifier() implementation on the same impl block, just assigning project_id to self.project_id.clone() is sufficient and would not break with your change, do you mind including this in your PR?

Great catch! Addressed in 607ae38

Ready for review

[kostas-petrikas]

Great catch! Addressed in 607ae38

Thank you,

The last request from me is to keep the function signatures the same without removing the async, to not introduce breaking changes to the API. I will simplify the signatures with a next big patch.

[Sydney-o9]

The last request from me is to keep the function signatures the same without removing the async, to not introduce breaking changes to the API. I will simplify the signatures with a next big patch.

Oops, should have anticipated that.. Updated in b1d8971