How Can I Securely Create Dynamic SQL Logins Using Stored Procedures?

Creating Dynamic SQL Logins

Developers often encounter difficulties when attempting to create SQL Logins dynamically using stored procedures. As a solution to this common issue, this article demonstrates how to construct dynamic logins using a straightforward and secure approach.

Problem Statement

A developer named Justin sought assistance in crafting a stored procedure that could both create a tenant in a SaaS database and grant it access to a predefined role. However, he encountered an error while attempting to create the login:

"CREATE LOGIN @username WITH PASSWORD = @password"

SQL Manager returned the following errors:

• "Incorrect syntax near '@username'."
• "Incorrect syntax near the keyword 'with'. If this statement is a common table expression, an XML namespaces clause, or a change tracking context clause, the previous statement must be terminated with a semicolon."

Answer

The key to resolving this issue lies in understanding that CREATE LOGIN only accepts literal values for the username. To address this, it is necessary to construct the login creation statement dynamically.

The following code demonstrates a safe approach:

DECLARE @sql nvarchar(max) = 'CREATE LOGIN ' + quotename(@username) + ' WITH PASSWORD = ' + quotename(@password, '''');
EXEC(@sql)

This approach wraps the literal username and password in quotename to prevent SQL injection attacks. By using a dynamic SQL statement and carefully handling the parameter values, it becomes possible to create SQL logins dynamically using stored procedures.

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