feat: support two-phase non-interactive firebase login

[joehan]

Description

Allows headless tools and AI agents to log the Firebase CLI into Google/Firebase in non-interactive environments using a two-phase login flow.

• Initiating firebase login --non-interactive generates a PKCE codeVerifier and sessionId, writes it to the local configstore, and outputs a login URL with a verification code instructions.
• Exchanging the code via firebase login <auth_code> retrieves the stored PKCE state, performs the remote token exchange, and records the active user session.

Before and After Command Outputs

Before

Running firebase login --non-interactive threw an error immediately:

Cannot run login in non-interactive mode. See login:ci to generate a token for use in non-interactive environments.

After

1. Initiating the login:

$ firebase login --non-interactive

To sign in to the Firebase CLI:

1. Take note of your session ID:

   97548

2. Visit the URL below on any device and follow the instructions to get your code:

   https://auth.firebase.tools/login?code_challenge=MgMej1pXyJBOCEl4o5VQ1zPAEF4JRgW6WCNHnH1lBfA&session=97548b2c-fe34-4813-9d9d-93827425952a&attest=lWAgfQyI5wQ491SwVqsd8JCGXKWgKacAab60RXJMSqQ

3. Complete the login by running:

   firebase login <authorizationCode>

2. Completing the login with the authorization code:

$ firebase login 4/0AdkVLPyTQOoo2mMMCsGpTl9ks_ozOmRGapvrd24bFQHaBmZ376AmaRNYx4nTs-HzU4Jnug
✔  Success! Logged in as joehanley@google.com

Scenarios Tested

• Initiating the login flow in non-interactive mode.
• Exchanging code with correct/matching state successfully.
• Exchanging code when no login state is present or state fails verification.
• Verified that full project listing commands (projects:list) works successfully post-authentication.

Sample Commands

firebase login --non-interactive
firebase login <authCode>

[gemini-code-assist]

Code Review

This pull request introduces support for a two-phase non-interactive authentication flow to firebase login using login [auth_code], allowing headless tools and agents to log in. It refactors the remote login logic in src/auth.ts into start and complete phases, updates the login command in src/commands/login.ts to handle these phases, and adds corresponding unit tests in src/commands/login.spec.ts. Feedback on the changes highlights a potential crash when accessing result.user.email without a truthiness check, and multiple violations of the repository style guide regarding the use of any as an escape hatch in error catch blocks and test assertions.

[gemini-code-assist]

Using any as an escape hatch in the catch block violates the repository style guide. We should catch the error as unknown and safely extract the message.

      } catch (e: unknown) {
        configstore.delete("tempLoginState");
        const message = e instanceof Error ? e.message : String(e);
        throw new FirebaseError("Login failed: " + message, { exit: 1 });
      }

References

1. Never use any or unknown as an escape hatch. Define proper interfaces/types or use type guards. ^(link)