Failures on code_verifier after upgrading our File Maker server

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1

getting failures on code_verifier after upgrading our File Maker server. Requiring end user to to do multiple attempts and then it is successful. This seems to be intermittent.

I checked the community https://community.auth0.com/t/failed-to-verify-code-verifier/99156 faq but didn’t see the page.

We’re in a pickle. Any help will be appreciated before we open a ticket. Thank you!

Here is a sample of the response:
{
“date”: “2026-09-18T15:04:25.923Z”,
“type”: “feacft”,
“description”: “Parameter ‘code_verifier’ is required”,
}

3

Hi @mike.birkhead

You are experiencing intermittent failures in your Auth0 PKCE (Proof Key for Code Exchange) flow after upgrading your FileMaker server. The error message indicates that the code_verifier parameter is missing during the token exchange step, requiring end users to retry multiple times before succeeding. You have checked the Auth0 community but could not find the specific FAQ page you referenced.

[Root Cause]

When calling the /authorize endpoint multiple times in quick succession, the error message above may be returned.

[Solution]

Avoid making more than one login request:

  • When making a login request, it saves the code_verifier in a cookie and sends the code_challenge to the /authorize endpoint.
  • If a login request is made multiple times, it will keep saving a new code_verifier, which will override the previous one. It will also keep sending the browser to a new authorize URL.
    • If this happens multiple times, the authorize URL with its code_challenge parameter will match the code_verifier cookie previously saved.

Ensure the app only calls the login method once to log in. Making a login request method multiple times in quick succession will be prone to errors (like the Invalid code verifier errors).

  • NOTE: The code challenge and the code_verifiers are different.

The following example demonstrates this error:

// This is ok
function login() {
  loginWithRedirect();
}

// This will be error prone
function login() {
  loginWithRedirect();
  loginWithRedirect();
  loginWithRedirect();
}

Additionally, the link you have posted currently has a public knowledge article on our support site. It talks about the Error “Failed to verify code verifier” after Users Authenticates in Application Using PKCE-enhanced Authorization Code Flow.

Let me know if this is the exact flow you are experiencing issues with or not.

Kind Regards,
Nik