Source code for keycloak.pkce_utils

#
# The MIT License (MIT)
#
# Copyright (C) 2017 Marcos Pereira <marcospereira.mpj@gmail.com>
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"""PKCE utility functions for code verifier and code challenge generation."""

import base64
import hashlib
import os




def generate_code_verifier(length: int = 128) -> str:
    """
    Generate a high-entropy cryptographic random string for PKCE code_verifier.

    RFC 7636 recommends a length between 43 and 128 characters.
    """
    return base64.urlsafe_b64encode(os.urandom(length)).rstrip(b"=").decode("utf-8")[:length]





def generate_code_challenge(code_verifier: str, method: str = "S256") -> tuple[str, str]:
    """
    Generate a code_challenge from the code_verifier using the specified method.

    Supported methods: "S256" (default), "plain".
    Returns (code_challenge, code_challenge_method).
    """
    if method == "S256":
        code_challenge = (
            base64.urlsafe_b64encode(hashlib.sha256(code_verifier.encode("utf-8")).digest())
            .rstrip(b"=")
            .decode("utf-8")
        )
        return code_challenge, "S256"
    if method == "plain":
        return code_verifier, "plain"
    error_msg = f"Unsupported PKCE method: {method}"
    raise ValueError(error_msg)