Failed Exchange Errors "Expected auth0-forwarded-for header to be a valid IP address"

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Problem statement

What causes a high volume of failed exchange errors with the following description?

Expected auth0-forwarded-for header to be a valid IP address

Cause

The header has to include a valid IPv4 or IPv6 address when used. If the client sends multiple or invalid formatted IPs with this header, Auth0 returns the “Expected auth0-forwarded-for header to be a valid IP address.” error.

Solution

The auth0-forwarded-for header is often sent with the resource owner password flow for notifying Auth0 with the user’s IP address logging into the application.

To resolve the issue, the server code should be updated to send a single valid IPv6 or IPv4 address.