I did not find any working clients for Linux that uses SSTP protocol, but for IKEv2 strongSwan provides a quite easily configurable and working solution.
To set up the VPN client I did the following:
1. Installed the strongswan-ikev2 package.
# apt-get install strongswan-ikev2
2. Configured the /etc/ipsec.conf file (changed the bold values):
# ipsec.conf - strongSwan IPsec configuration file
# basic configuration
# Add connections here.
rightid="C=XX, ST=State, L=Location, O=Organization, OU=OrgUnit, CN=CommonName, E=email"
3. Set up the password for the user name in the /etc/ipsec.secrets file:
username : EAP "password"
4. Put the certificate of the Certificate Authory into the /etc/ipsec.d/cacerts/ directory to trust the certificates which was created by this CA:
# mv CA.cer /etc/ipsec.d/cacerts/
5. Restart ipsec:
# /etc/init.d/ipsec restart
6. To run the VPN connection type:
# ipsec up companyvpn
7. Use the VPN connection.
8. To stop the VPN connection type:
# ipsec down companyvpn