jwt: Add JWT support for minio server.

Please read JWT.md before using this feature.

vendor/github.com/dgrijalva/jwt-go/signing_method.go

@@ -0,0 +1,24 @@
+package jwt
+
+var signingMethods = map[string]func() SigningMethod{}
+
+// Implement SigningMethod to add new methods for signing or verifying tokens.
+type SigningMethod interface {
+	Verify(signingString, signature string, key interface{}) error // Returns nil if signature is valid
+	Sign(signingString string, key interface{}) (string, error)    // Returns encoded signature or error
+	Alg() string                                                   // returns the alg identifier for this method (example: 'HS256')
+}
+
+// Register the "alg" name and a factory function for signing method.
+// This is typically done during init() in the method's implementation
+func RegisterSigningMethod(alg string, f func() SigningMethod) {
+	signingMethods[alg] = f
+}
+
+// Get a signing method from an "alg" string
+func GetSigningMethod(alg string) (method SigningMethod) {
+	if methodF, ok := signingMethods[alg]; ok {
+		method = methodF()
+	}
+	return
+}