Currently the K2 Webservice Endpoint broker does not support Security Username Token authentication; at the moment this is only implemented for WCF Endpoint broker.

With the WCF Endpoint broker, once successfully configured and registered, you have to pass in the username token every time you execute a SmO method against the registered service -- sure, you can put this in a variable field or maybe even an environment filed but this is very static in nature. In other words if or when you change the password information for the underlying service account you will need to update the serialized complex string value with the updated username token value across multiple solutions i.e. workflows forms, views, etc. This can be painstaking in larger implementations.
For this kind of scenarios there should be an option to allow this to flow down from the service instance level similar to the "Default HTTP Request Headers" service key.

So, this is a two part feature request:

1. Support for Security Username Token authentication with the Webservice Endpoint broker

2. Option for a "Default Security Username Token" service key in the service instance configuration.