add initial auth0 module

auth/auth0/authenticator/errors.go

@@ -0,0 +1,9 @@
+package authenticator
+
+import "fmt"
+
+var ErrEmptyDomain = fmt.Errorf("domain cannot be empty")
+var ErrEmptyClientID = fmt.Errorf("client id cannot be empty")
+var ErrEmptyClientSecret = fmt.Errorf("client secret cannot be empty")
+var ErrEmptyRedirectURI = fmt.Errorf("redirect uri cannot be empty")
+var ErrNoIDToken = fmt.Errorf("no id_token field in oauth2 token")