codeChallengeMethod property
The method used to encode the code_verifier for the code_challenge parameter. This SHOULD be S256, but the spec allows the use of plain if for some reason the client cannot support SHA256. If excluded, code_challenge is assumed to be plaintext if codeChallenge is included. Microsoft identity platform supports both plain and S256. For more information, see the PKCE RFC. This is required for single page apps using the authorization code flow.
Implementation
final String? codeChallengeMethod;