[keycloak-user] External Registration Flow

I have an existing application that I'm looking to integrate with keycloak. One of the flows we're working on is a user self-registration flow. In this flow, a user will enter registration information, then the user will be provisioned within the local app and then we use web service calls to create the user in keycloak. After the user is provisioned, then we do a SAML post to keycloak, the user logs in and then they are redirected back to our app. This is all working fine, however, the user must enter their username and password twice, once on the registration screen and once to log into keycloak to establish an SSO session. We'd like to avoid using the keycloak registration screens since we collect additional business data on our registration screen that our app needs. Are there any suggestions on how to avoid this double login?