signature should be populated after parsing a valid token

parser.go

@@ -98,7 +98,8 @@ func (p *Parser) Parse(tokenString string, keyFunc Keyfunc) (*Token, error) {
 	}
 
 	// Perform validation
-	if err = token.Method.Verify(strings.Join(parts[0:2], "."), parts[2], key); err != nil {
+	token.Signature = parts[2]
+	if err = token.Method.Verify(strings.Join(parts[0:2], "."), token.Signature, key); err != nil {
 		vErr.err = err.Error()
 		vErr.Errors |= ValidationErrorSignatureInvalid
 	}

parser_test.go

@@ -184,9 +184,11 @@ func TestParser_Parse(t *testing.T) {
 				if e := err.(*jwt.ValidationError).Errors; e != data.errors {
 					t.Errorf("[%v] Errors don't match expectation.  %v != %v", data.name, e, data.errors)
 				}
-
 			}
 		}
+		if data.valid && token.Signature == "" {
+			t.Errorf("[%v] Signature is left unpopulated after parsing", data.name)
+		}
 	}
 }