SQL Server Documentation

Authentication Methods

SQL Server supports several authentication methods to verify the identity of users connecting to the server:

• Windows Authentication (Integrated Security): This is the recommended authentication mode. It uses the security credentials of a Windows user account or a Windows group to log in to SQL Server. This simplifies management by leveraging existing Windows security infrastructure.
• SQL Server Authentication (Mixed Mode): In this mode, users authenticate using a unique login ID and password that are stored within SQL Server itself. This is useful for non-Windows environments or when specific SQL Server logins are required. It's crucial to use strong, unique passwords for SQL Server logins.
• Azure Active Directory Authentication: For cloud-based deployments, SQL Server can integrate with Azure Active Directory (now Microsoft Entra ID) for centralized identity management and authentication.

Login vs. User

It's important to understand the distinction between logins and users:

• Login: A login grants access to the SQL Server instance itself. Logins are server-level principals. They can be Windows users/groups or SQL Server logins.
• User: A user is a database-level principal that is associated with a login. Users are granted permissions within specific databases. A single login can be mapped to users in multiple databases.

The process typically involves creating a server-level login and then mapping it to a database-level user within the desired database.

Access Control and Permissions

Once authenticated, access to data and objects within SQL Server is controlled by a granular permission system:

• Permissions: These are specific rights granted to users or roles to perform actions on securable objects (e.g., `SELECT` on a table, `EXECUTE` on a stored procedure). Permissions can be granted, denied, or revoked.
• Roles: Roles are collections of permissions that can be assigned to users. SQL Server provides built-in fixed server roles (e.g., `sysadmin`, `securityadmin`) and fixed database roles (e.g., `db_owner`, `db_datareader`). You can also create custom database roles.
• Securables: These are the objects within SQL Server that permissions can be applied to. Examples include servers, databases, schemas, tables, views, stored procedures, and functions.

Best Practices

• Always use Windows Authentication when possible.
• Enforce strong password policies for SQL Server Authentication logins.
• Grant the principle of least privilege: users and roles should only have the permissions they absolutely need.
• Regularly review login accounts and user permissions.
• Disable or remove unused logins.
• Utilize roles to simplify permission management.
• Consider implementing auditing to track access and changes.

SQL Examples

Here are some basic T-SQL examples for managing logins and users:

-- Creating a SQL Server Login
CREATE LOGIN [MyNewLogin] WITH PASSWORD = 'A_Very_Strong_Password123!',
    DEFAULT_DATABASE = [master],
    CHECK_EXPIRATION = ON,
    CHECK_POLICY = ON;
GO

-- Granting access to a database
USE [MyDatabase];
GO
CREATE USER [MyNewUser] FOR LOGIN [MyNewLogin];
GO

-- Granting SELECT permission on a table
GRANT SELECT ON OBJECT::[dbo].[MyTable] TO [MyNewUser];
GO

-- Adding a user to a database role
ALTER ROLE db_datareader ADD MEMBER [MyNewUser];
GO

For detailed syntax and options, refer to the T-SQL documentation for CREATE LOGIN, CREATE USER, and GRANT statements.

Further Reading

• SQL Server Security Architecture
• Understanding SQL Server Roles
• Best Practices for SQL Server Security