feat: Add method to obtain ID Token using Refresh Token in Admin SDK

[inakam]

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[REQUIRED] Step 2: Describe your environment

• Operating System version: macOS Sonoma 14.5
• Firebase SDK version: v4.14.1
• Library version: v4.14.1
• Firebase Product: auth

[REQUIRED] Step 3: Describe the problem

I am implementing authentication using Session Cookies following the documentation at https://firebase.google.com/docs/auth/admin/manage-cookies.

Since Session Cookies can only be valid for a maximum of 2 weeks, they need to be refreshed periodically. However, the SDK does not provide functionality to obtain an ID Token using a Refresh Token.

As an alternative, I've implemented a solution using the REST API described in https://firebase.google.com/docs/reference/rest/auth#section-refresh-token to refresh the token. However, I believe having this functionality built into the SDK would be more convenient.

Would it be possible to add a feature to the SDK that allows obtaining an ID Token using a Refresh Token?