As per the word Authentication, it’s the process of verification whether someone using the particular utility or thing is the actual user or not. This verification is called as authentication.
There are different mechanism exists for authentication, for applications generally we use user login and password for authentication process.
SQL Server has two type of Authentication.
1. SQL Server Authentication
2. Windows Authentication
3. Mixed Mode Authentication
SQL Server Authentication: User will be provided separate user name and password for SQL Server and can be login in to SQL server using that only.
Windows Authentication: User can login in to SQL Server using windows login i.e. SQL Server automatically take the user’s window login and use it as login credentials for SQL Server.
Mixed Mode: you can use both windows and SQL Server Authentication to login into SQL Server.
For SQL Server authentication mode you can decide on your security need.
SQL Server Quest 