OAuth2 provides client applications a 'secure delegated access' to server resources on behalf of a resource owner. Or you can allow users to sign in to your application with their GitLab.com account.
In fact OAuth allows to issue access token to third-party clients by an authorization server,
with the approval of the resource owner, or end-user.
Mostly, OAuth2 is using for SSO (Single sign-on). But you can find a lot of different usages for this functionality.
For example, our feature 'GitLab Importer' is using OAuth protocol to give an access to repositories without sharing user credentials to GitLab.com account.
Also GitLab.com application can be used for authentication to your GitLab instance if needed [GitLab OmniAuth](gitlab.md).
GitLab has two ways to add new OAuth2 application to an instance, you can add application as regular user and through admin area. So GitLab actually can have an instance-wide and a user-wide applications. There is no defferences between them except the different permission levels.
### Adding application through profile
Go to your profile section 'Application' and press button 'New Application'
After this you will see application form, where "Name" is arbitrary name, "Redirect URI" is URL in your app where users will be sent after authorization on GitLab.com.
