OAuth

OAuth is a feature by which users can sign in with a third party intermediary authorization. For example, if you were at a online printing store and wanted to print photos from an album in another website, the printing store can retrieve the photos from that website on your behalf and you can continue with your print order, if you sign in to that website.It differs from login in that you don't have to repeatedly provide username and password for different websites. The sign in on one website can be reused for others.
The way this works is by providing users access tokens based on third party referral. This token grants a user access to resources. The token may expire every few minutes and may need to be refreshed. So a refresh token can be requested. Admins to OAuth provider can see which users have registered from which clients. They can also revoke access to users and clients.
OAuth has four different workflows for granting access: These are :
Implicit Grant – such as when the mobile application follows a redirect to the client application.
Credentials Grant – such as when the user provides username and password for a token
Client Credentials Grant – such as when admin applications from secured kiosks provide context regardless of the user
Refresh Grant – a client can retrieve an access token by exchanging a previous refresh token.

An access token request consists of the following
- a grant type aka authorization code
- code
- redirect URI
- client Id
while the response consists of
- a return type ( data or redirect )
- Access Token
- token type
- refresh type
- expires in how many seconds
- refresh token
- scope

The authorization request consists of response type, client id, scope and state. The response consists of code and state.