add google login

- refactor resolvers
- fix signup method typos

Resolves #17

server/constants/oauthInfoUrls.go

@@ -0,0 +1,10 @@
+package constants
+
+var (
+	// Ref: https://github.com/qor/auth/blob/master/providers/google/google.go
+	GoogleUserInfoURL = "https://www.googleapis.com/oauth2/v3/userinfo"
+	// Ref: https://github.com/qor/auth/blob/master/providers/facebook/facebook.go#L18
+	FacebookUserInfoURL = "https://graph.facebook.com/me?access_token="
+	// Ref: https://docs.github.com/en/developers/apps/building-github-apps/identifying-and-authorizing-users-for-github-apps#3-your-github-app-accesses-the-api-with-the-users-access-token
+	GithubUserInfoURL = "https://api.github.com/user"
+)