I haven't heard of this happening, but if Shopify supports OIDC or SAML v2 you can use an IdP config.
https://fusionauth.io/docs/v1/tech/identity-providers/openid-connect/ documents it for instance. It appears Shopify supports OAuth so the OIDC provider should work.
Important things to note:if you need to pass additional parameters to certain endpoints, turn off 'discover endpoints' and you can add them. See https://fusionauth.io/community/forum/topic/663/force-google-account-selection-on-every-login?_=1612454251976 for more the token returned by the external OAuth provider will be available on user.registrations[x].tokens with the key of the provider id. See https://fusionauth.io/docs/v1/tech/apis/identity-providers/openid-connect/ for more details the links above are for OIDC, but SAML integrations are also supported; review the analogous documentation.