I've seen you're using the most dangerous connection string possible.

This is absolutely the wrong way to connect to a database.

Create a SQL login limited to the database the application needs access to. Create a group within the database and put that SQL login into that group.

Allow only access to the group and the stuff that's really needed. E.g., specifically name the tables/views the app has SELECT permissions and/or the sprocs the app is allowed to execute.

Once you're able to connect to the database using Management Studio and the login you just created, change the connection string to the new login.

Another option:

If this is an Intranet solution, you could also change the connection string to use a trusted connection (=Windows authentication).

Ask your domain admins to create an AD group for users that are allowed to use the application.

At the SQL Server side, add the AD group to the SQL group and you should be all set.