Shared-user model

Expanded Definition

The shared-user model is a B2B identity pattern in which a person uses one global account across multiple tenants, while tenant membership and authorization determine what they can do inside each tenant. It is common in SaaS because it reduces account duplication, lowers onboarding friction, and simplifies cross-tenant navigation. In NHI and IAM discussions, the model matters because the authentication boundary is broader than the tenant boundary, so a compromise or misconfiguration in the global identity can affect multiple customer environments. That makes it different from a tenant-scoped identity model, where each tenant maintains a more isolated account lifecycle and trust boundary. Guidance varies across vendors on how tightly this should be coupled to single sign-on, shared sessions, or cross-tenant directories, so implementation details are still evolving. For policy design, the relevant baseline is least privilege and explicit access control, consistent with NIST Cybersecurity Framework 2.0. The most common misapplication is treating the shared login as harmless convenience, which occurs when organisations let a global account become the de facto master key across tenants.

Examples and Use Cases

Implementing the shared-user model rigorously often introduces a governance tradeoff: it improves usability and supportability, but it also concentrates blast radius, requiring organisations to weigh operational simplicity against tenant isolation.

• A customer success manager signs in once and switches between multiple enterprise tenants under the same global account, with each tenant enforcing separate membership and role mapping.
• A managed service provider uses one identity to administer several client tenants, but privilege assignment is constrained per tenant to avoid cross-customer access leakage.
• A SaaS platform relies on a shared-user pattern for multi-tenant navigation, then pairs it with strong session controls and audit logging to preserve traceability.
• An identity team reviews the pattern against the governance expectations described in the Ultimate Guide to NHIs when global authentication state begins to overlap with automation or shared credentials.
• A security architect compares the design to federation and zero trust expectations in the NIST Cybersecurity Framework 2.0 before approving broad tenant access.

Why It Matters in NHI Security

The shared-user model becomes a security concern when people, sessions, or connected automations inherit access beyond the tenant they should control. In practice, the model can blur accountability, complicate offboarding, and create hidden lateral movement paths if a compromised global account is trusted across many tenants. That is especially dangerous where organisations already struggle to understand identity sprawl: NHI Mgmt Group reports that only 5.7% of organisations have full visibility into their service accounts, a signal that many environments lack the inventory discipline needed to notice when shared identity patterns are expanding risk. Even though the model is often presented as a user-experience choice, it can also affect how secrets, tokens, and delegated access are governed across tenants. The right control posture is to separate authentication convenience from authorisation scope, then prove that tenant boundaries still hold under compromise, offboarding, and incident response. Organisaties typically encounter the consequences only after a tenant-wide access review, credential compromise, or noisy cross-tenant incident, at which point the shared-user model becomes operationally unavoidable to address.

Related resources from NHI Mgmt Group

• Why do shared API keys create the wrong trust model for AI agents?
• What breaks when agents rely on shared credentials or borrowed user identities?
• What breaks when customer identity is forced into a shared platform model?
• Who should own PAM in a shared IT and security model?