Username is not saved in openconnect VPN connection dialog

gnome-shell's network agent doesn't send all secrets returned by the openconnect authentication dialog to NM and so the username entered in the openconnect VPN dialog is not saved.

How to reproduce:

• Run a test server:
  • Clone the openconnect repository: git://git.infradead.org/users/dwmw2/openconnect.git
  • Build with: ./autogen.sh ; ./configure ; make check
  • sudo dnf install ocserv
  • sudo ocserv -f -c tests/configs/test-user-pass.config
• Connect first time:
  • nmcli connection add type vpn con-name oc vpn.service-type openconnect vpn.data "gateway = 127.0.0.1"
  • Connect to the 'oc' VPN through the GUI
  • Enter 'test' username and 'test' password
  • Disconnect from VPN
• Connect second time:
  • Connect to the 'oc' VPN through the GUI
  • Observe that the username was not saved

This is the connection returned from the gnome-shell agent to NM:

...
'vpn': {
 ...,
 'secrets':
  <{'gwcert': 'pin-sha256:xp3scfzy3rOQsv9NcOve/8YVVv+pHr4qNCXEXrNl5s8=',
    'cookie': 'zfH/5JSKROo4SopwWdjnzslrBswZ3UHpSPIQEbi6kso=',
    'lasthost': '127.0.0.1:443',
    'gateway': '127.0.0.1:443'}>,
}

Compare it with from the connection returned by nm-applet:

'vpn': {
 ...,
 'secrets':
 <{'lasthost': '127.0.0.1:443',
   'cookie': 'FS6LWmKlnvYgxpYaIQHTppbC6juk5dpT4Xmla6ccnos=',
   'form:main:username': 'test',
   'gwcert': 'pin-sha256:xp3scfzy3rOQsv9NcOve/8YVVv+pHr4qNCXEXrNl5s8=',
   'gateway': '127.0.0.1:443',
   'certificate:127.0.0.1:443': 'pin-sha256:xp3scfzy3rOQsv9NcOve/8YVVv+pHr4qNCXEXrNl5s8='}>,
}

NetworkManager bug report: https://gitlab.freedesktop.org/NetworkManager/NetworkManager/issues/328