The IdentityServerTools class is a collection of useful internal tools that you might need when writing extensibility code for IdentityServer. To use it, inject it into your code, e.g. a controller:

public MyController(IdentityServerTools tools)
    _tools = tools;

The IssueJwtAsync method allows creating JWT tokens using the IdentityServer token creation engine. The IssueClientJwtAsync is an easier version of that for creating tokens for server-to-server communication (e.g. when you have to call an IdentityServer protected API from your code):

public async Task<IActionResult> MyAction()
    var token = await _tools.IssueClientJwtAsync(
        clientId: "client_id",
        lifetime: 3600,
        audiences: new[] { "backend.api" });

    // more code