Canada SSO: adapt login to common flow provided in external_auth.
Fix #3176 wrong login/password error message.

Now shows `Sorry, unrecognized username or password`, not `Unexpected login error`.
Merge pull request #3176 from sergii-tkachenko/DS-379_canada-common-auth-module-login

Canada SSO: adapt login to common flow provided in external_auth.
Closes #3156 - enable DS Shipment for Canada
Merge pull request #3198 from aaronschachter/canada_shipment

Enable DS Shipment for Canada