We are users of Salesforce Communities, we create content with Salesforce CMS and publish on our Community and send the content as an email. Could we do it? How could we do it?

We have generated an apex SOAP web service that must be invoked from an external system. By request of the external system the request must be made in a single step (using UsernameToken, including username and password in the header of the call).
If I try to test using SOAPui, it returns:
sf:INVALID_SESSION_ID
INVALID_SESSION_ID: Invalid Session ID found in SessionHeader: Illegal Session
This  article describes how to perform using a Marketing Cloud user: https://developer.salesforce.com/docs/atlas.en-us.mc-apis.meta/mc-apis/authenticate-soap-api.htm (https://developer.salesforce.com/docs/atlas.en-us.mc-apis.meta/mc-apis/authenticate-soap-api.htm)
What configuration must be done to configure it with a user with a Salesforce license? Can it be replicated for a user with a Salesforce license?
 

We have generated an apex SOAP web service that must be invoked from an external system. By request of the external system the request must be made in a single step (using UsernameToken, including username and password in the header of the call).
If I try to test using SOAPui, it returns:
sf:INVALID_SESSION_ID
INVALID_SESSION_ID: Invalid Session ID found in SessionHeader: Illegal Session
This  article describes how to perform using a Marketing Cloud user: https://developer.salesforce.com/docs/atlas.en-us.mc-apis.meta/mc-apis/authenticate-soap-api.htm (https://developer.salesforce.com/docs/atlas.en-us.mc-apis.meta/mc-apis/authenticate-soap-api.htm)
What configuration must be done to configure it with a user with a Salesforce license? Can it be replicated for a user with a Salesforce license?