Pkce.Challenge
val make : Verifier.t -> t
Will always be a S256 challenge https://www.rfc-editor.org/rfc/rfc7636#section-4.2
val of_string : transformation:transformation -> string -> t
val to_code_challenge_and_method : t -> string * string
https://www.rfc-editor.org/rfc/rfc7636#section-4.3