Getting Started with OAuth2 in Go

Alex Pliutau

Published in

ITNEXT

2 min readJun 11, 2019

This is a text version of this video: packagemain #11: Getting started with OAuth2 in Go.

Getting started with OAuth2 in Go

Authentication usually is very important part in any application. You can always implement your own authentication system, but it will require a lot of work, registration, forgot password form, etc. That’s why OAuth2 was created, to allow user to log in using one of the many accounts user already has.

In this video we’ll create a simple web page with Google login using oauth2 Go package.

Google Project, OAuth2 keys

First of all, let’s create our Google OAuth2 keys.

Go to Google Cloud Platform
Create new project or use an existing one
Go to Credentials
Click “Create credentials”
Choose “OAuth client ID”
Add authorized redirect URL, in our case it will be localhost:8080/callback
Get client id and client secret
Save it in a safe place

How OAuth2 works with Google

Obtain OAuth 2.0 credentials from the Google API Console.
Obtain an access token from the Google Authorization Server.
Send the access token to an API.
Refresh the access token, if necessary.

Structure

We’ll do everything in 1 main.go file, and register 3 URL handlers:

/
/login
/callback

Initial handlers and OAuth2 config

go get golang.org/x/oauth2

We save google client id and secret in env variables and only use os.Getenv in the code.

/

Now let’s render an HTML on index page.

/login

We send random state string. In our cause it’s not random.

/callback

check state
use code to get token
use token to get user info

Test it

go run main.go

Conclusion

That’s all what we need to do to integrate OAath2 with Google in Go. As you can see, it’s only 70 lines of code.

Also, there is a nice package https://github.com/markbates/goth from Mark Bates which provides multi-provider authentications.

Full code.