Azure identity needs a "whoami" function.

[cbare]

Greetings,

Is your feature request related to a problem? Please describe.
Debugging Azure permissions is often very confusing, especially in least-permissions scenarios where you don't have access to the environment. I want to be sure my code is running with the correct managed identity.

Describe the solution you'd like
A function along the lines of this:

credential = DefaultAzureCredential()
principal_details = azure.identity.whoami(credential)
logger.info('Authenticated as: %s %s', principal_details.name, principal_details.client_id)

This would help identify misconfiguration, especially in the unfortunate case where a different team manages the environment in which the code runs.

[cbare]

My very smart friend, GPTo3 gave me this bit of code. Maybe something similar would make a good addition to azure.identity?

import base64
import json


TOKEN_SCOPE = "https://management.azure.com/.default"

def whoami(cred, scope=TOKEN_SCOPE):
    """
    Get information about the identity represented by the credential.
    Returns a dictionary with tenant, client_id, object_id, user, audience, and issued_by.
    """
    token = cred.get_token(scope).token
    payload_b64 = token.split(".")[1]                   # <header>.<payload>.<sig>
    # add missing padding and decode
    padded = payload_b64 + "=" * (-len(payload_b64) % 4)
    claims = json.loads(base64.urlsafe_b64decode(padded))

    return {
        "tenant": claims.get("tid"),
        "client_id / appid": claims.get("appid"),       # service principal or MI client-id
        "object_id": claims.get("oid"),                 # object-id of that identity
        "user": claims.get("upn"),                      # only present for user tokens
        "audience": claims.get("aud"),
        "issued_by": claims.get("iss"),
    }