A credential is a record that contains the authentication information (credentials) required to connect to a resource outside of SQL Server. This information is used internally by SQL Server. Most credentials contain a Windows user name and password.
The information stored in a credential allows a user that has connected to SQL Server 2005 via SQL Server Authentication to access resources outside of the server instance. When the external resource is Windows, the user is authenticated as the Windows user specified in the credential. A single credential can be mapped to multiple SQL Server logins. However, a SQL Server login can be mapped to only one credential.
System credentials are created automatically and are associated with specific endpoints. Names for system credentials start with two hash signs (##).
To view information about credentials, see the sys.credentials catalog view.
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14 April 2006