Using SQL Server Application Roles through C#

I've not had to do this with C# before (did it with Delphi no problem), and found that there is an issue using connection pooling.

The problem is that the connection seems to be in error once a role has been set. The test I performed was as follows :

1. Set approle
2. call a stored procedure to populate a datatable from c#
3. call the stored procedure again.

On the second call to the stored procedure, I got an error whatever I did. If you do not set the approle, you will get a permission denied error. If you set the approle then you get a nasty looking error telling you the connection needs to be reset. Either way doesn't work.

As I am reluctant to use a dedicated connection (for a start this would involve rewriting alot of code, not to mention any performance issues), I needed a proper solution. And here it is :

1. Open connection.
2. exec sp_setapprole
3. run sql
4. exec sp_unsetapprole
5. close connection.

The only tricky bit is that you have to get the @cookie from sp_setapprole and pass it into sp_unsetapprole to free it up. This is a varbinary, so needs to be handled in a byte[] type.

So, pseudo-ish code is

public DataSet getSomeData()
{
connection = getConnection();
connection.Open();
byte[] cookie = SetApprole(connection, approle, approlepassword);
....
call some sql using connection
....

UnsetApprole(connection, cookie);
}

public byte[] SetApprole(SqlConnection connection, string approle, string approlePassword)
{
StringBuilder sqlText = new StringBuilder();

sqlText.Append("DECLARE @cookie varbinary(8000);");
sqlText.Append("exec sp_setapprole @rolename = '" + approle + "', @password = '" + approlePassword + "'");
sqlText.Append(",@fCreateCookie = true, @cookie = @cookie OUTPUT;");
sqlText.Append(" SELECT @cookie");

if (connection.State.Equals(ConnectionState.Closed))
connection.Open();

using (SqlCommand cmd = connection.CreateCommand())
{
cmd.CommandType = CommandType.Text;
cmd.CommandText = sqlText.ToString();
cmd.CommandTimeout = commandTimeout;
return (byte[])cmd.ExecuteScalar();
}
}

And the final trick - calling sp_unsetapprole. This gave me issues as it errored with a 15422 (Application roles can only be activated at the ad hoc level) on a CommandType.Text execution. It has to be a CommandType.StoredProcedure to work :

public void UnsetApprole(SqlConnection connection, byte[] approleCookie)
{
string sqlText = "exec sp_unsetapprole @cookie=@approleCookie";

if (connection.State.Equals(ConnectionState.Closed))
connection.Open();

using (SqlCommand cmd = connection.CreateCommand())
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = "sp_unsetapprole";
cmd.Parameters.AddWithValue("@cookie", approleCookie);

cmd.CommandTimeout = commandTimeout;
cmd.ExecuteNonQuery();
}
}

Remember to add all your favourite try...catch blocks etc.