RFC 7636: Proof Key for Code Exchange by OAuth Public Clients (part 3/3)
https://datatracker.ietf.org/doc/html/rfc7636
The "S256" method protects against eavesdroppers observing or intercepting the "code_challenge", because the challenge cannot be used without the verifier. With the "plain" method, there is a chance that "code_challenge" will be observed by the attacker on the device or in the ht…