[FEATURE] Expose token validation function to allow for custom implementations

[amorey]

Is there an existing feature request for this?

• I have searched the existing feature requests

Is your feature request related to a problem? Please describe.

I'm unable to use an origin check to validate WebSocket upgrade requests so I want to protect against cross-site WebSocket hijacking attacks by using CSRF token validation.

Describe the solution that you would like.

I would like the library to expose the token validation function so I can use the validation logic in my own method.

Describe alternatives you have considered.

Currently, I'm formulating POST requests on the fly configured with the initial HTTP GET upgrade request's credentials and passing them through a csrf protection instance ServeHTTP() method.

Anything else?

Great library! Thanks for all your work!