resolving attribute based on ACS URL

[Andrew Morgan]

We have requests to enable SAML authentication for multiple Slack 
instances.  Slack's documentation gives these parameters for configuring 
the IDP:

- SSO post-back URL (also known as the Assertion Consumer Service URL):
     https://yourteamname.slack.com/sso/saml

- Entity ID: https://slack.com


Since there would be multiple integrations using the same entityID, I'm 
looking for another method to handle attribute release and authorization 
(an intercept to block access if the user is not a member of a particular 
group).

Is it possible to use the ACS URL provided in the SAML authn request as a 
condition in attribute resolution?

Are there other ways to approach this problem?

Thanks,
 	Andy