When integrating Salesforce with high-security enterprise systems like an Enterprise Billing System (EBS) and a Document Management System (DMS), the primary architectural concern is respecting the Enterprise security needs for access control. These systems often contain highly sensitive financial data and are governed by strict regulatory requirements (e.g., PCI-DSS or GDPR).

The integration consultant must evaluate how to extend existing enterprise identity and authorization policies to Salesforce users. This often involves a Identity Federation strategy using protocols like SAML 2.0 or OpenID Connect. Instead of maintaining separate credentials in Salesforce (which Option A suggests and is generally an "anti-pattern" for 10 million records), the consultant should consider using a central Identity Provider (IdP).

By considering enterprise security needs, the architect ensures that when a support agent clicks a link in Salesforce to view a bill, the request is authenticated against the enterprise's security gateway. This allows for Single Sign-On (SSO) while ensuring that authorization (who can see what) remains mastered in the source systems or the central IdP. Migration (Option C) is physically and technically unfeasible for systems handling 10 million customers' historical bills and real-time processing. The focused objective is to build a "window" into these systems from Salesforce while maintaining the integrity of the enterprise's existing security perimeter.