How do I set up a Web Service so that I can use it in the Workflow Manager?

The following is a basic guide on how to set up a Web Service so that it can be used in the Workflow Manager.

First, copy the files of the Web Wervice to the server on which you want to host the web service. Make sure that the Web Server (IIS) role is installed on the server.

Open the "Internet Information Services (IIS)-Manager" and navigate to the Application Pools menu. Right-click to add a new application pool. 

In the following menu a significant name should be assigned. As soon as the application pool has been created, the identity should be checked and, if necessary, adjusted using the extended settings. The identity represents the user with whom the application pool is executed. When selecting the identity, make sure that this user has the necessary rights to the directory in which the Web Service is stored. The user rights that are actually required vary from Web service to Web Service. Read permissions on the files in the directory are mandatory, whereas write permissions are only required if the Web Service changes files.

The next step is to add a new application. Open the menu item "Sites". A new application can be added by right-clicking on the website under which the Web Service is to run (for example, "Default Web Site").

In the menu choose a suitable name, the application pool that you want to use, and the directory in which the Web Service is stored.

To open the Web Service, switch to the "Contents" view, select the .asmx file and click "Browse" in the right column. This opens the Web Service in the browser.

You can test the methods in the browser and also read the URL under which the Web Service can be accessed. This is usually structured as follows:

To be able to use the Web Service in the workflow, open the Workflow Designer and select the workflow in which you want to integrate the Web Service. Add a new Web Service activity to the workflow. In this activity you must first enter a name and the address under which the Web Service can be reached. Use the URL that was displayed in the browser in the previous step as the address.

Click on "Find methods" to check whether the web service is accessible and then to display the available methods in the drop-down menu.
If the Web Service is changed in the background, it is necessary to reload the methods.

The basic requirements that a Web Service must meet in order to be used in the workflow are explained here.
An exemplary Web Service can be found here.