**Access to Single Sign-On (SSO) is currently available as an add-on for users with a Pro level subscription. If you would like to subscribe to Pro, you can do so in your subscription settings at Admin > Settings > Subscription and Billing.
What is single sign-on?
Single sign-on (SSO) is a protocol for authenticating an existing user to comment without registering for a global Disqus account. This assumes that you have an proprietary database of users already established.
What's SSO good for?
SSO is valuable for keeping existing users - It allows users in your own database to comment without forcing them to register with Disqus.
Can I use SSO on multiple sites?
Yes, but it is only possible to create one remote domain per user account, and we recommend using a single remote domain per site. If you require an additional remote domain, please create an additional user account for which we can enable SSO.
Single sign-on docs
Technical implementation details for SSO
A collection of code examples in PHP, Ruby, C#, Java, Scala, Python, Coldfusion and Node/Meteor
SSO instructions when using the Disqus Wordpress plugin
How to effectively troubleshoot SSO issues
How to post to Disqus using SSO for authentication