What does error validating access token mean?

The error “error validating access token” typically means there is an issue with the access token being used to authorize access to an API or service. Access tokens are used to grant access to protected resources without exposing user credentials. When you get this error, it indicates the access token is invalid or malformed in some way, so the API/service cannot validate it.

Common Causes of the Error

There are a few common reasons you may encounter this error:

The access token has expired – Access tokens are usually issued with a short lifetime, often just minutes or hours. If the lifetime has passed, the token is no longer valid.

The access token has been revoked – The issuing authority may have revoked the token for security reasons, rendering it invalid.
The access token is malformed – An error in generating or transmitting the access token could result in it being malformed and unreadable by the API/service.
The access token is for a different API/service – Access tokens are typically issued for specific APIs/services. If you are trying to use an access token with the wrong API/service, it will fail validation.

There are underlying authentication/authorization issues – Sometimes this error occurs due to problems on the authentication server or in the authorization workflow that prevent proper token generation.

How to Fix the Error

Depending on the specific cause, there are a few things you can try to resolve this error:

Request a new access token – If the token expired or was revoked, requesting a fresh token from the issuing authority will often resolve the issue.

Double check the token value – Make sure the access token value you are providing matches the issued token. An incorrect value will fail validation.
Verify the token scope – Check that the token was issued for the API/service you are trying to access. Tokens are typically issued for specific scopes.
Review the authorization flow – Look for any issues with the authorization process that obtains the access token. Fixing problems here can help.

Check for clock skew – If different systems have inaccurate clocks, it can cause tokens to expire early. Synchronizing system clocks may help.

Additionally, checking API logs, documentation, and any available technical support can provide clues to help troubleshoot the specific problem.

Common Scenarios Causing This Error

Some typical use cases where you may encounter an “error validating access token” error include:

Using an Expired OAuth Token

OAuth access tokens commonly expire after a set period, often an hour. If you try to reuse an expired OAuth token, the API/service will fail to validate it and return this error. Always check token expiration and request fresh tokens when needed.

Revoked OAuth Refresh Token

If an OAuth refresh token used to obtain new access tokens is revoked, issuing new access tokens will fail. Check that the refresh token has not been revoked and request a new one if needed.

Using a Token After Logout

Once you log out of an application, any existing access tokens may be invalidated. Attempting API calls with those tokens after logout can result in this error. Logging in again to acquire new tokens is required.

Accessing the Wrong API

Access tokens are typically issued for accessing specific APIs/services. Using a token intended for API A to access API B will often fail with this error. Double check the API you are calling matches the token.

Malformed JWT Token

If the access token is in JWT format, any parsing or encoding issues can cause the contained data to become malformed. This leads to failed validation by the API. Fixing the JWT generation process can address this.

Steps to Debug the Error

Here are some steps you can take to help debug this error:

Examine the access token format – See if it is an opaque string, JWT, etc. The format provides clues about validation.
Check the expiration time – If a JWT, decode the payload and look at the exp claim. Compare to the current time.
Review authorization logs – Errors during authorization may cause malformed tokens. Logs can reveal issues.

Trace request/response payloads – Inspect request headers and response contents between clients, identity providers, and APIs.
Reproduce the issue with Postman – Helps rule out application code issues by isolating the API call.

Example Root Causes

Here are some concrete examples of issues that could lead to this error:

Expired OAuth Access Token

The access token used in the API call expired an hour ago. Need to request a new access token using refresh token.

Client Secret Changed

The client secret used to generate the access token was recently rotated. Existing tokens are now invalid until re-generated with the new secret.

Invalid API Gateway Configuration

The JWT verification logic on the API Gateway has an incorrect allowed audience value, causing it to fail JWT validation.

Access Token Scrambling

A proxy between the client and API is corrupting the access token value, leading to scrambled junk being validated.

How to Prevent This Error

Some best practices that can help avoid this error include:

Give access tokens short expiration times – Reduces validity of leaked/lost tokens.

Rotate client secrets periodically – Forces generation of new access tokens.
Extensively test authorization workflows – Helps identify edge cases that cause malformed tokens.
Set up monitoring and alerting – Get notified immediately if token validation failures occur.

Add request logging – Logs facilitate troubleshooting and identifying problematic requests.
Follow OAuth 2.0 best practices – Properly implementing OAuth improves overall security.

Troubleshooting Questions

When troubleshooting this error, here are some useful questions to ask:

Where in the flow does the failure occur? Client, identity provider, or API?
Does the token format look correct? Verify expected JWT/opaque string structure.
Is the token expiration time valid? Check against current time.

What OAuth grant flow is being used? Authorization code? Client credentials?
Are any components experiencing connectivity or availability issues?
Have there been any recent configuration changes like secret rotation?

Are their errors or warnings in related logs? Any relevant stack traces?

Mitigating the Impact

Some ways to mitigate the impact of this error include:

Automatically requesting fresh tokens – Refresh tokens can get new access tokens if expired.

Gracefully handling authorization failures – Display friendly error messaging to users if refresh also fails.
Monitoring token issuance endpoints – Get alerted if token issuance traffic spikes or fails.
Retrying failed requests with new tokens – Transparently re-attempt API call if initial token is invalid.

Using short-lived access tokens – Tokens only valid for minutes reduces damage from leaks.

Example Log Messages

Here are some example log/error messages you may see with this issue:

401 Unauthorized Error

  HTTP Status 401 - Invalid access token
  type Status report
  description Invalid access token

Nginx Proxy Error

  2022/10/14 17:45:33 [error] 23#23: *1 upstream sent invalid status 401 while reading response header from upstream

API Gateway Access Log

  {
    "requestId": "c6af9ac6-7b61-11e6-9a41-93e8deadbeef",
    "ip": "192.168.1.1",
    "requestUrl": "/orders",
    "status": "401",
    "errorMessage": "Access token invalid" 
  }

Conclusion

In summary, the “error validating access token” error occurs when an access token is rejected as invalid by the API/service you are calling. Potential causes include expired, revoked or malformed tokens, calling the wrong API, and issues in the authorization process. Carefully inspecting tokens, reviewing authorization workflows, monitoring systems, and following OAuth best practices can help avoid and troubleshoot these access token validation failures.