I assign the role manually from ume idm console, then try the searchRequest, also cannot found the assigned roles attribute get returned, then I guess it's the sapuser schema issue. not sure what need to do to extend the schema.
<spml:searchRequest xmlns:spml='urn:oasis:names:tc:SPML:1:0' xmlns:dsml='urn:oasis:names:tc:DSML:2:0:core'>
<spml:searchBase type='urn:oasis:names:tc:SPML:1:0#GUID'>
<spml:id>sapuser</spml:id>
</spml:searchBase>
<dsml:filter>
<dsml:equalityMatch name='logonname'>
<dsml:value>Test125</dsml:value>
</dsml:equalityMatch>
</dsml:filter>
<spml:attributes>
<dsml:attribute name='firstname'/>
<dsml:attribute name='lastname'/>
<dsml:attribute name='assignedroles'/>
<dsml:attribute name='allassignedroles'/>
<dsml:attribute name='assignedgroups'/>
<dsml:attribute name='allassignedgroups'/>
</spml:attributes>
</spml:searchRequest>
<spml:searchResponse xmlns:spml='urn:oasis:names:tc:SPML:1:0' xmlns:dsml='urn:oasis:names:tc:DSML:2:0:core' result='urn:oasis:names:tc:SPML:1:0#success'>
<spml:searchResultEntry>
<spml:identifier type='urn:oasis:names:tc:SPML:1:0#GenericString'>
<spml:id>USER.R3_DATASOURCE.TEST125</spml:id>
</spml:identifier>
<spml:attributes>
<dsml:attr name='firstname'>
<dsml:value>Test124</dsml:value>
</dsml:attr>
<dsml:attr name='lastname'>
<dsml:value>Li</dsml:value>
</dsml:attr>
</spml:attributes>
</spml:searchResultEntry>
</spml:searchResponse>
success