Sign in with Coinbase OAuth2 Security Best Practices
Storing Credentials Securely
You should take great care to ensure your credentials are stored securely. If someone obtains your access_token with the wallet:transactions:send permission, s/he will be able to send all the bitcoin, litecoin or ethereum out of your account.
You should avoid storing API keys in your code base (which gets added to version control). The recommended best practice is to store them in environment variables. Separating credentials from your code base and database is always good practice.
OAuth2 access tokens and refresh tokens should be stored encrypted, with the encryption key stored in environment variables. To increase the security of your OAuth2 implementation, you should always specify a state parameter, request moderate wallet:transactions:send limits and implement 2FA authentication.
State Variable
To help protect against cross-site request forgery (CSRF), we recommended that you include a state GET parameter during the OAuth2 authorization process. Verifying that this variable matches upon receipt of an authorization code will mitigate CSRF attempts. Make sure that you use a string that is at least 8 characters long.
An example of a request with state is as follows:
https://login.coinbase.com/oauth2/auth?response_type=code&client_id=YOUR_CLIENT_ID&redirect_uri=YOUR_CALLBACK_URL&scope=user+balance&state=CSRFToken123
Once user has authorized your application, the same state param will be passed back via the redirect url with code param. You can read more about it here.
OAuth2 Redirect URI
For added security, all redirect_uris must use SSL (i.e. begin with https://). URIs without SSL can only be used for development and testing and will not be supported in production.
Validating SSL Certificates
It is also very important that your application validates our SSL certificate when it connects over https. This helps prevent a man in the middle attack. If you are using a client library, this may be turned on by default, but you should confirm this. Anytime you see a setting to 'verify SSL' you should ensure it is set to true.