When making calls to Amazon's S3 and similar services a "signature" value needs to be generated.
http://docs.aws.amazon.com/AmazonS3/latest/API/Welcome.html
The details of the signing required are documented here
http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-auth-using-authorization-header.html
Currently this can only be accomplished with a convoluted mechanism of groovy scripts. It would be very useful if (upon entering the relevant credentials) SoapUI could generate the signature value and populate the relevant header.