DataSourceKeyResolver

I wish to implement a DataSourceKeyResolver on my DevForce BOS. I have created the class which implements IDataSourceKeyResolver. wish This class  will lookup the Database connection string in the Database and return the connection string based on the keyName and keyExtension. I wish to use a DevForce Entitymanager to return the required connection string. My application does not allow anonymous access so i must use an authenticated EM to perform the query. I don't seem to able to create the EM on the server side that is logged in. I must be missing something obvious here so would you mind showing me the code required to perform this. Here is my current code that is not working
   private static String GetConnectionString(string keyName, string keyExtension) 
    {
        try
        {
            Log.Information("LEAF_DataKeyResolver", "GetConnectionString", keyName + "  +  " + keyExtension);
            ConfigInfoEntities context = new ConfigInfoEntities();

            LEAFConfig_DocumentDatabases connection = context.LEAFConfig_DocumentDatabases
                .Where(c => c.DatabaseName == keyExtension)
                .First();

            Log.Information("LEAF_DataKeyResolver", "GetConnectionString", connection.ConnectionString);

            return connection.ConnectionString;
        }
        catch (Exception ex)
        {
            Log.Error("LEAF_DataKeyResolver", "GetConnectionString", ex.Message);
            return "";
        }

    }