Security Token Service in Sharepoint 2010

What is actually Security Token Ser开发者_StackOverflowvice? Why it is required to change web config of STS for enabling a farm based authentication site in Shrepoint 2010?

The Security Token Service is built on the Windows Identity Foundation Framework. This service is responsible for issuing, managing, and valadating security tokens. During the authentication process, using Classic or Claims based authentication, a token is generated, consumed by SharePoint and then converted into an SPUser object for authorization.

You need to update the STS site in SharePoint because this is the service that generates the tokens, and the providers must be specified such that the service knows what it can try to authenticate against, either AD, an FBA database, or both.

There is a more detailed explanation of the function of the STS service and its architecture located here.