Problem to obtain an access token when using SSO

Is there a way to obtain an access token when using SSO (Shibboleth)?

When I try to get the access token using this command (for SSO user):
curl -d “username=myssouser@mydomain.com” -d “password=123456” https://mydomain.com/api2/auth-token/

I get in response:
{“non_field_errors”:[“Unable to login with provided credentials.”]}

When I try to get the access token for non SSO user:
curl -d “username=myuser@mydomain.com” -d “password=123456” https://mydomain.com/api2/auth-token/

after above command I get the proper access token:
{“token”:“3a248b7b27d3…”}