(Feat): Initial Commit

internal/util/oauth2/pkce.go

@@ -0,0 +1,35 @@
+package oauth2
+
+import (
+	"crypto/sha256"
+	"encoding/base64"
+	"fmt"
+
+	"allaboutapps.dev/aw/go-starter/internal/util"
+)
+
+const (
+	defaultVerifierLength = 128
+)
+
+func GetPKCECodeVerifier() (string, error) {
+	// for details regarding possible characters in verifier, see:
+	// https://tools.ietf.org/html/rfc7636#section-4.1
+	verifier, err := util.GenerateRandomString(defaultVerifierLength, []util.CharRange{util.CharRangeNumeric, util.CharRangeAlphaLowerCase, util.CharRangeAlphaUpperCase}, "-._~")
+	if err != nil {
+		return "", fmt.Errorf("failed to generate random string: %w", err)
+	}
+
+	return verifier, nil
+}
+
+func GetPKCECodeChallengeS256(verifier string) string {
+	// for details regarding transformation of verifier to challenge see:
+	// https://tools.ietf.org/html/rfc7636#section-4.2
+	// base64 encoding must be unpadded, URL encoding:
+	// https://tools.ietf.org/html/rfc7636#page-17
+	sum := sha256.Sum256([]byte(verifier))
+	b64 := base64.RawURLEncoding.EncodeToString(sum[:])
+
+	return b64
+}