return an error if the requested hash method hasn't been compiled in

hmac.go

@@ -47,6 +47,10 @@ func (m *SigningMethodHMAC) Verify(signingString, signature string, key interfac
 		var sig []byte
 		var err error
 		if sig, err = DecodeSegment(signature); err == nil {
+			if !m.Hash.Available() {
+				return ErrHashUnavailable
+			}
+
 			hasher := hmac.New(m.Hash.New, keyBytes)
 			hasher.Write([]byte(signingString))
 
@@ -62,6 +66,10 @@ func (m *SigningMethodHMAC) Verify(signingString, signature string, key interfac
 
 func (m *SigningMethodHMAC) Sign(signingString string, key interface{}) (string, error) {
 	if keyBytes, ok := key.([]byte); ok {
+		if !m.Hash.Available() {
+			return "", ErrHashUnavailable
+		}
+
 		hasher := hmac.New(m.Hash.New, keyBytes)
 		hasher.Write([]byte(signingString))
 

jwt.go

@@ -23,6 +23,7 @@ type Keyfunc func(*Token) (interface{}, error)
 // Error constants
 var (
 	ErrInvalidKey      = errors.New("Key is invalid or of invalid type.")
+	ErrHashUnavailable = errors.New("The requested Hash function is unavailable")
 )
 
 // A JWT Token.  Different fields will be used depending on whether you're

rsa.go

@@ -67,6 +67,9 @@ func (m *SigningMethodRSA) Verify(signingString, signature string, key interface
 	}
 
 	// Create hasher
+	if !m.Hash.Available() {
+		return ErrHashUnavailable
+	}
 	hasher := m.Hash.New()
 	hasher.Write([]byte(signingString))
 
@@ -91,7 +94,12 @@ func (m *SigningMethodRSA) Sign(signingString string, key interface{}) (string,
 	default:
 		return "", ErrInvalidKey
 	}
+
 	// Create the hasher
+	if !m.Hash.Available() {
+		return "", ErrHashUnavailable
+	}
+
 	hasher := m.Hash.New()
 	hasher.Write([]byte(signingString))