gSoap fault SOAP-ENV:MustUnderstand[no subcode] - visual-c++

Question

I am building a web service for ONVIF camera using gSoap.
I have generated the header and the source files using the core wdsl provided by ONVIF at https://www.onvif.org/profiles/specifications/.
However, every time i make a request from the client i get the below error in the function soap_begin_serve(soap):
SOAP 1.2 fault SOAP-ENV:MustUnderstand[no subcode]
"The data in element 'Security' must be understood but cannot be processed"
What does the above error means and how can i fix it?
EDIT: This is what i receive at the camera side:
POST / HTTP/1.1
Content-Type: application/soap+xml; charset=utf-8; action="http://www.onvif.org/ver10/device/wsdl/GetSystemDateAndTime"
Host: localhost:8090
Content-Length: 261
Accept-Encoding: gzip, deflate
Connection: Close
<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope"><s:Body xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><GetSystemDateAndTime xmlns="http://www.onvif.org/ver10/device/wsdl"/></s:Body></s:Envelope>POST / HTTP/1.1
Content-Type: application/soap+xml; charset=utf-8; action="http://www.onvif.org/ver10/device/wsdl/GetScopes"
Host: localhost:8090
Content-Length: 905
Accept-Encoding: gzip, deflate
Connection: Close
<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope"><s:Header><Security s:mustUnderstand="1" xmlns="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd"><UsernameToken><Username>admin</Username><Password Type="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-username-token-profile-1.0#PasswordDigest">WFz21zL8rch8LRoxAPzgHRMBbr0=</Password><Nonce EncodingType="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-soap-message-security-1.0#Base64Binary">9y79ka0xD02oCIw6GAoIPwEAAAAAAA==</Nonce><Created xmlns="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd">2017-05-21T08:15:58.902Z</Created></UsernameToken></Security></s:Header><s:Body xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><GetScopes xmlns="http://www.onvif.org/ver10/device/wsdl"/></s:Body></s:Envelope>

Answer 1

SOAP 1.2 fault SOAP-ENV:MustUnderstand[no subcode]
"The data in element 'Security' must be understood but cannot be processed"
This means that you will need to enable WS-Security to authenticate:
add #import "wsse.h" to the .h header file (aka. service and data binding "interface file") for soapcpp2 to process.
in your source code, #include "plugin/wsseapi.h"
in your source code, provide the user credentials before sending the request with soap_wsse_add_UsernameTokenDigest(soap, NULL, "username", "password");
compile the source code with compiler flag -DWITH_OPENSSL and compile your application code base together with plugin/wsseapi.c, plugin/smdevp.c, and plugin/mecevp.c (the plugin directory is in the gSOAP distro path), and of course also compile stdsoap2.c or stdsoap2.cpp and other generated files;
link with OpenSSL -lssl -lcrypto, and perhaps -lz if compression is desired;
when using the full WS-Security plugin capabilities with gSOAP (digital signature and/or encryption), you should compile all your source code with compiler option -DWITH_OPENSSL -DWITH_DOM -DWITH_GZIP and also compile dom.c or dom.cpp together with your code.
See also the WS-Security plugin for gSOAP.
Hope this helps.