code: function doLogin() {
  	// Request the login page.
  	let res = http.get(baseURL + "/user/login");
  	check(res, {
  		"title is correct": (res) => res.html("title").text() == "User account | David li commerce-test",
  	});
  
  	// TODO: Add attr() to k6/html!
  	// Extract hidden input fields.
  	let formBuildID = res.body.match('name="form_build_id" value="(.*)"')[1];
  
  	group("login", function() {
  		// Pick a random set of credentials.
  		let creds = credentials[Math.floor(Math.random()*credentials.length)];
  
  		// Create login request.
  		let formdata = {
  			name: creds.username,
  			pass: creds.password,
  			form_build_id: formBuildID,
  			form_id: "user_login",
  			op: "Log in",
  		};
  		let headers = { "Content-Type": "application/x-www-form-urlencoded" };
  		// Send login request
  		let res = http.post(baseURL + "/user/login", formdata, { headers: headers });
  		// Verify that we ended up on the user page
  		check(res, {
  			"login succeeded": (res) => res.url == `${baseURL}/users/${creds.username}`,
  		}) || fail("login failed");
  	});
  }
docs: Request the login page and perform a user login