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The S4S Leads Security Connector is an option that facilitates authentication into your Sitecore website using login credentials stored in a Salesforce lead record.This This functionality overrides both the Membership and Role providers used by Sitecore so that the information is only stored in Salesforce.
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Authenticating users against Leads and Contacts only works using multi-role and will not work using single-rolethe Single-Role option (because Leads are not associated with an Account). Only the Multi-Role option can be used.