Support webauthn (#17957)

Migrate from U2F to Webauthn

Co-authored-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

vendor/github.com/duo-labs/webauthn/protocol/challenge.go

@@ -0,0 +1,27 @@
+package protocol
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+)
+
+// ChallengeLength - Length of bytes to generate for a challenge
+const ChallengeLength = 32
+
+// Challenge that should be signed and returned by the authenticator
+type Challenge URLEncodedBase64
+
+// Create a new challenge to be sent to the authenticator. The spec recommends using
+// at least 16 bytes with 100 bits of entropy. We use 32 bytes.
+func CreateChallenge() (Challenge, error) {
+	challenge := make([]byte, ChallengeLength)
+	_, err := rand.Read(challenge)
+	if err != nil {
+		return nil, err
+	}
+	return challenge, nil
+}
+
+func (c Challenge) String() string {
+	return base64.RawURLEncoding.EncodeToString(c)
+}