switch to maintained lib (#16532)

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

vendor/github.com/golang-jwt/jwt/rsa.go

@@ -0,0 +1,101 @@
+package jwt
+
+import (
+	"crypto"
+	"crypto/rand"
+	"crypto/rsa"
+)
+
+// Implements the RSA family of signing methods signing methods
+// Expects *rsa.PrivateKey for signing and *rsa.PublicKey for validation
+type SigningMethodRSA struct {
+	Name string
+	Hash crypto.Hash
+}
+
+// Specific instances for RS256 and company
+var (
+	SigningMethodRS256 *SigningMethodRSA
+	SigningMethodRS384 *SigningMethodRSA
+	SigningMethodRS512 *SigningMethodRSA
+)
+
+func init() {
+	// RS256
+	SigningMethodRS256 = &SigningMethodRSA{"RS256", crypto.SHA256}
+	RegisterSigningMethod(SigningMethodRS256.Alg(), func() SigningMethod {
+		return SigningMethodRS256
+	})
+
+	// RS384
+	SigningMethodRS384 = &SigningMethodRSA{"RS384", crypto.SHA384}
+	RegisterSigningMethod(SigningMethodRS384.Alg(), func() SigningMethod {
+		return SigningMethodRS384
+	})
+
+	// RS512
+	SigningMethodRS512 = &SigningMethodRSA{"RS512", crypto.SHA512}
+	RegisterSigningMethod(SigningMethodRS512.Alg(), func() SigningMethod {
+		return SigningMethodRS512
+	})
+}
+
+func (m *SigningMethodRSA) Alg() string {
+	return m.Name
+}
+
+// Implements the Verify method from SigningMethod
+// For this signing method, must be an *rsa.PublicKey structure.
+func (m *SigningMethodRSA) Verify(signingString, signature string, key interface{}) error {
+	var err error
+
+	// Decode the signature
+	var sig []byte
+	if sig, err = DecodeSegment(signature); err != nil {
+		return err
+	}
+
+	var rsaKey *rsa.PublicKey
+	var ok bool
+
+	if rsaKey, ok = key.(*rsa.PublicKey); !ok {
+		return ErrInvalidKeyType
+	}
+
+	// Create hasher
+	if !m.Hash.Available() {
+		return ErrHashUnavailable
+	}
+	hasher := m.Hash.New()
+	hasher.Write([]byte(signingString))
+
+	// Verify the signature
+	return rsa.VerifyPKCS1v15(rsaKey, m.Hash, hasher.Sum(nil), sig)
+}
+
+// Implements the Sign method from SigningMethod
+// For this signing method, must be an *rsa.PrivateKey structure.
+func (m *SigningMethodRSA) Sign(signingString string, key interface{}) (string, error) {
+	var rsaKey *rsa.PrivateKey
+	var ok bool
+
+	// Validate type of key
+	if rsaKey, ok = key.(*rsa.PrivateKey); !ok {
+		return "", ErrInvalidKey
+	}
+
+	// Create the hasher
+	if !m.Hash.Available() {
+		return "", ErrHashUnavailable
+	}
+
+	hasher := m.Hash.New()
+	hasher.Write([]byte(signingString))
+
+	// Sign the string and return the encoded bytes
+	if sigBytes, err := rsa.SignPKCS1v15(rand.Reader, rsaKey, m.Hash, hasher.Sum(nil)); err == nil {
+		return EncodeSegment(sigBytes), nil
+	} else {
+		return "", err
+	}
+}