Background

A web service(or webservice) is a method of communication between two points over a network. In a web context this most typically means a REST or SOAP based request via tcp/ip i.e. over HTTP or HTTPS.

DotNetNuke

As an asp.net application, DotNetNuke supports all of the expected .net based webservices such as asp.net webservices (ASMX) and WCF . However with asmx werbservices there is one item to watch out for. As DotNetNuke inspects all .net mapped requests (such as aspx/asmx/axad/ashx) to determine if a user has changed portals (and expires their role cookie if they have), an asmx page can end up with the user being logged out. To avoid this situation the asmx should be in one of the following folders (or a subfolder of one of them) - "admin", "controls", "desktopmodules", "mobilemodules", "premiummodules", "providers"

DNN 7 does support web services for client side code based on MS WebAPI 1, while DNN 8 uses WebAPI 2. See DNN 7 and DNN 8 development guides for details.

References

• Running a webservice inside of a DotNetNuke site - this blog demonstrates an alternative to the suggested workaround for asmx webservices detailed above.
• IWeb - IWEB allows you to create Web Services for your DotNetNuke Portal. You simply upload the module and start adding your own methods.
  Intergrates with DNN authentication and API
• DotNetNuke webservice examples
• Creating secure DotNetNuke ajax asp.net webservices
• Creating RESTful JSON webservices with DotNetNuke