Part 4

In this part we will enable authentication with a Google mail address.

Start with installing and importing the goth and gorilla sessions packages, among the imports add:
  "github.com/markbates/goth"
  "github.com/markbates/goth/gothic"
  "github.com/markbates/goth/providers/google"
  "github.com/gorilla/sessions"


We will also need uuid functionality so
go get github.com/satori/go.uuid
and add the library to imports, you may have to add the identifier uuid:
  uuid "github.com/satori/go.uuid"


Next let's set up our handle functions. We need one for the callback:
func callback(res http.ResponseWriter, req *http.Request) {
  user, err := gothic.CompleteUserAuth(res, req)
  if err != nil {
    fmt.Println("Error in CompleteUserAuth: ", err)
    fmt.Fprintln(res, err)
    return
  }
  session, err := gothic.Store.Get(req, "session")
  if err != nil {
    fmt.Println("Error getting session: ", err)
    http.Error(res, err.Error(), http.StatusInternalServerError)
    return
  }
  id := uuid.NewV4()
  session.Values["uuid"] = id.String()
  session.Values["Name"] = user.Name
  session.Values["Email"] = user.Email
  err = session.Save(req, res)
  if err != nil {
    fmt.Println("Error saving session: ", err)
  }
  http.Redirect(res, req, "/chat/", http.StatusSeeOther)
}


One for logging out:
func logout(res http.ResponseWriter, req *http.Request) {
  gothic.Logout(res, req)
  session, _ := gothic.Store.Get(req, "session")
  session.Values["Email"] = ""
  session.Values["Name"] = ""
  session.Values["uuid"] = ""
  session.Save(req, res)
  res.Header().Set("Location", "/")
  res.WriteHeader(http.StatusSeeOther)
}


As well as one for authenticating:
func authenticate(res http.ResponseWriter, req *http.Request) {
  gothic.BeginAuthHandler(res, req)
}


Next let's add routes for our functions:
  router.HandleFunc("/auth/{provider}/callback", callback)
  router.HandleFunc("/logout/{provider}", logout)
  router.HandleFunc("/auth/{provider}", authenticate)


Now it is time to get api keys from Google, go to https://console.developers.google.com

Create a new project then click on credentials and create credentials then OAuth cliend ID. Select Web application as application type and as redirect URI put http://127.0.0.1:8080/auth/google/callback

Hit create and copy the client ID and secret into the top of the main function like so:
  key := "abc"         // Replace with your SESSION_SECRET or similar
  maxAge := 86400 * 30 // 30 days
  isProd := false      // Set to true when serving over https

  store := sessions.NewCookieStore([]byte(key))
  store.MaxAge(maxAge)
  store.Options.Path = "/"
  store.Options.HttpOnly = true // HttpOnly should always be enabled
  store.Options.Secure = isProd

  gothic.Store = store

  goth.UseProviders(
    google.New("YOUR API KEY HERE", "YOUR API SECRET HERE", "http://127.0.0.1:8080/auth/google/callback", "email", "profile"),
  )


Next we add the login and logout links to our navlist in base.gohtml:
<li><a href="/auth/google">Log in</a></li>
<li><a href="/logout/google">Log out</a></li>


Now we have to add some lines to the serveChat function:
  session, err := gothic.Store.Get(r, "session")
  if session.Values["Name"] != nil &&session.Values["Name"] != "" {
    data.Name = session.Values["Name"].(string)
  }


Finally we modify chat.gohtml:
   <h1>Welcome to the chat app, {{ .Name }}</h1>


To make everything work we also need to create a file named go.mod and paste the following there:
module auth

go 1.13

require (
  github.com/markbates/goth v1.64.0
  github.com/satori/go.uuid v1.2.0 // indirect
  go.mongodb.org/mongo-driver v1.4.3 // indirect
)


Now we can go run *.go and then go to 127.0.0.1:8080 and enjoy our log in system! Note that localhost:8080 wont work. As usual the full code can be found at https://github.com/jhlq/gocourse/tree/main/part4

Updated on 2020-11-30.