Portainer fails to start with "invalid url for trusted origin" error

Issue

• Portainer fails to start and logs a fatal error such as:

  failed to build server | error="invalid url for trusted origin. Please check the trusted origins flag. trusted_origin: \"portainer.example.com\""

• After startup, browser requests return 403 Forbidden on state-changing actions, with CSRF check failed entries in the server logs.

Cause

As of Portainer version 2.41, CSRF protection has been migrated from gorilla/csrf to Go's standard library. This is a breaking change to how trusted origins are validated. Each entry in PORTAINER_TRUSTED_ORIGINS must now be a full URL including scheme (http or https). Bare hostnames are no longer accepted. Optionally, a port may also be included.

Format	Valid?
portainer.example.com	No longer accepted
https://portainer.example.com	Valid
https://portainer.example.com:9443	Valid

Solution

Update all entries in your PORTAINER_TRUSTED_ORIGINS configuration (CLI flag or environment variable) to use full URLs with scheme.