To install the AutoTask API in your project, add the nuget package:
AutoTask.Api
To execute a query using the AutoTask query language, use code as follows:
var client = new Client(autoTaskCredentials.Username, autoTaskCredentials.Password);
var version = await client.GetVersion();
var result = await client
.ExecuteQueryAsync("<queryxml><entity>Account</entity><query><field>id<expression op=\"greaterthan\">0</expression></field></query></queryxml>")
.ConfigureAwait(false);
Contributions welcome!