The DefaultSubjectProvider does not set “subjectNameIDFormat" to formats other than unspecified. It needs to set the format correctly based on the type of principal.
Refer to the screenshots below that contain an example of a possible fix for CXF versions: 3.0.6-3.1.X and CXF versions: 3.0.5 and below respectively:
Screenshot from CXF 3.0.5 and below: Shows code from getSubject()
Screenshot from CXF 3.0.6 +: Shows code from createSubjectBean()