Methods of Denying login by specific SQL Authenticated user using Management Studio
Connecting to management studio should not be that threat to you unless and until that user gets full read/write on the database in question which needs to be secured.

You can use DENY VIEW ANY DATABASE Permission herewhich will make the DB sort of invisible for that user when he tries to connect via SSMS, however if they are smart enough and hit a query with USE &lt;database name&gt; they can proceed.

Else, its better you just give them access via windows authentication (with controlled access) and do not share any SQL login credentials which have the permission to execute the task which you do not want the user to.

Also, read this thread