Cloud-to-Cloud Integration: Authentication Errors Despite Correct OAuth Setup

[sairajennifer]

Hello everyone,

I am currently working on a Cloud-to-Cloud integration for Google Home using the Smart Home Developer framework. Even after completing the full setup, I am facing persistent authentication issues that I haven’t been able to resolve.

Issue Description

After successfully setting up the Google Cloud project, enabling the required APIs, and configuring OAuth, all API requests are still returning a 401 Unauthorized response. The error messages indicate invalid or expired credentials, even though the OAuth flow appears to complete correctly.

Troubleshooting Steps Already Taken

• Regenerated OAuth Client ID and Client Secret

• Ensured the Smart Device Management API and required services are enabled

• Verified OAuth scopes

• Checked server time synchronization (NTP)

• Revalidated redirect URIs multiple times

Unfortunately, the issue persists.

Questions for the Community

1. Are there any known pitfalls or common mistakes in the OAuth authentication flow for Cloud-to-Cloud integrations?

2. Do additional IAM roles or service account permissions need to be explicitly assigned?

3. Are there recommended debugging tools, logs, or endpoints to better trace authentication failures?

Any guidance, best practices, or shared experiences would be greatly appreciated.

Thank you in advance for your help!

Additional note:
For reliable services and professional support in Switzerland, you may also check out Professional Cleaning Company Zurich:

[arm_dpe · Accepted solution]

Thanks for reaching out, To solve this problem we need to focus on 3 areas:  OAuth Protocol Compliance, Project Environment, and Permissions.

1. OAuth Response Compliance.

Google’s Smart Home framework is strict about the format of the JSON returned by your token exchange endpoint. Even a small syntax deviation causes a silent 401 failure.

• Data Types: Ensure expires_in is an Integer (e.g., 3600), not a String ("3600").
• Required Fields: Your response must include "token_type": "Bearer".
• Headers: Your token endpoint must return the Content-Type: application/json header and ideally Cache-Control: no-store.
• Client Authentication: Ensure your backend supports receiving the client_id and client_secret via HTTP Basic Auth or POST body parameters, as Google may use either depending on the library version.

2. Project Status & Account Settings

The state of your Google Cloud project can override even perfectly written code.

• "Testing" vs. "Production": If your OAuth Consent Screen is in "Testing" mode, refresh tokens expire after 7 days. If your issue started a week after setup, this is likely the cause. Switch it to "Production" to ensure long-lived tokens.
• Sync Intent Requirements: Ensure the HomeGraph API is enabled. Without it, the initial SYNC intent may fail, which the Google Home app often misreports as an authentication error.
• User Linking: Verify that the account you are using to link in the Google Home app is added as a Test User in the OAuth Consent Screen (if still in testing mode).

3. Permissions & IAM Roles

Even if the user is authenticated, your backend service might lack the authority to talk to Google's HomeGraph.

• Service Account Roles: The service account used for Request Sync and Report State must have the Owner role. Ensure the service account has the Service Account OpenID Connect Identity Token Creator role.
• OAuth Scopes: Ensure the scopes requested in the Actions Console (e.g., https://www.googleapis.com/auth/homegraph) exactly match the scopes configured in your Google Cloud OAuth consent screen.

4. Direct Debugging Actions

Tool	What to look for
GCP Logs Explorer	Query for resource.type="assistant_action_project" and check for OPEN_AUTH_FAILURE.
Google Home Test Suite	Run the Authentication tests to see if the error occurs during code-to-token exchange.
JWT Decoder	If using JWTs, ensure the aud (audience - https://oauth2.googleapis.com/token) and iss (issuer) fields are correct.

Let me know if any of these helped.