Support the token-less developer experience (omit developer-token header)

[abddeen]

Feature request

Please add support for the token-less developer experience so that developers enrolled in that program can run this MCP
server without setting GOOGLE_ADS_DEVELOPER_TOKEN.

Under the token-less program, requests to the Google Ads API are authenticated entirely via OAuth and the developer-token header should be omitted (or the requirement waived) for approved Google Cloud projects.

Current behavior

GOOGLE_ADS_DEVELOPER_TOKEN is mandatory. In ads_mcp/utils.py:

• _get_developer_token() raises ValueError("GOOGLE_ADS_DEVELOPER_TOKEN environment variable not set.") when the env var is missing.
• _get_googleads_client() always passes developer_token into GoogleAdsClient(...).

There is no flag, env var, or config option to disable this, so token-less program participants cannot use the server as-is.

Proposed behavior

• Treat GOOGLE_ADS_DEVELOPER_TOKEN as optional.
• When unset (or when an explicit opt-in like GOOGLE_ADS_TOKENLESS=1 is provided), construct the client without the developer token and ensure the developer-token header is not attached to outgoing requests.
• Document the token-less mode in the README alongside the existing auth options.

Notes / open questions

• The underlying google-ads-python GoogleAdsClient currently requires developer_token as a constructor argument, so this likely needs either (a) a workaround that constructs the client with a placeholder and
  strips the header in an interceptor (similar to the existing MCPHeaderInterceptor), or (b) a direct REST/gRPC call path that bypasses GoogleAdsClient for token-less users. Guidance from maintainers on the
  preferred approach would be appreciated.

Use case

Participants in the token-less program are not expected to provision or manage a developer token, so the current hard requirement blocks them from using this official MCP server.