Shared API tokens break accountability first. Once one token is reused across people or scripts, the action trail no longer maps cleanly to a single identity, and revocation becomes blunt rather than targeted. The result is access that may still work after the original user’s intent has changed.
Why Shared API Tokens Break MCP Governance
MCP access built on shared API tokens creates a false sense of simplicity. The token becomes the identity, so every caller looks the same to the server, the audit log, and any downstream enforcement. That collapses attribution, makes intent invisible, and turns revocation into a broad outage instead of a precise response. It also creates hidden persistence: once the token is copied into a script, ticket, or config file, it can outlive the user, the workflow, or the original business need.
This is exactly the pattern highlighted in the Guide to the Secret Sprawl Challenge, where duplicated secrets and informal sharing make recovery far harder than teams expect. OWASP also treats shared secrets as a structural weakness in OWASP Non-Human Identity Top 10 because they undermine lifecycle control and accountability at the identity layer. In practice, many security teams discover this only after a token leak, not during design review.
What Changes When MCP Uses Per-Caller Identity Instead
MCP works much better when each caller has its own workload identity and each action is authorized at runtime. The important shift is from “who knows the token” to “what is this caller, what is it trying to do, and is that allowed right now.” For autonomous or semi-autonomous tools, that usually means short-lived credentials, token exchange, and policy decisions that include context such as tool, scope, environment, and task state.
Current guidance suggests three practical controls:
- Use unique identities per agent, service, or user workflow rather than shared tokens.
- Issue just-in-time credentials with short TTLs and automatic revocation after task completion.
- Evaluate access at request time with policy-as-code instead of hard-coding broad static scopes.
That model aligns with the OWASP Agentic AI Top 10 and the SPIFFE approach to workload identity, where the goal is cryptographic proof of what the caller is, not just possession of a reusable secret. It also reflects the accountability concerns covered in Ultimate Guide to NHIs, where lifecycle discipline is as important as initial issuance. The 2025 State of NHIs and Secrets in Cybersecurity reported by Entro Security found that 91% of former employee tokens remain active after offboarding, showing how shared credentials routinely survive the people who were supposed to own them.
These controls tend to break down in legacy MCP deployments that only support one global bearer token because the server cannot distinguish caller intent, session boundaries, or least-privilege scope.
Where Shared Tokens Still Appear, and Why the Edge Cases Matter
Tighter token scoping often increases operational overhead, requiring teams to balance safer identity boundaries against integration complexity. That tradeoff is real in fast-moving MCP environments, especially where teams have many scripts, bots, and developer tools that were built around one shared secret.
Best practice is evolving, but there is no universal standard for every MCP deployment yet. Shared tokens still show up in early-stage internal tools, ephemeral sandboxes, and vendor integrations that have not adopted workload identity. The problem is that these environments often become production-adjacent without the control maturity to match.
Two edge cases matter most. First, a shared token used only inside one team is still risky if that team includes multiple humans, automation, or agents, because the action trail is still ambiguous. Second, even if the token is rotated frequently, rotation alone does not restore identity attribution or stop lateral reuse inside a running process. The better pattern is to couple OAuth 2.0 Token Exchange with explicit workload identity and narrow MCP permissions, then treat any shared secret as a temporary migration state rather than a steady-state design.
That is why incidents like the Salesloft OAuth token breach matter to MCP practitioners: once a token is reusable across contexts, compromise becomes scalable instead of contained.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Non-Human Identity Top 10, OWASP Agentic AI Top 10 and CSA MAESTRO address the attack and risk surface, while NIST AI RMF and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Non-Human Identity Top 10 | NHI-01 | Shared tokens erase identity boundaries and break attribution for non-human callers. |
| OWASP Agentic AI Top 10 | A1 | Agentic systems need runtime authorization, not static shared secrets. |
| CSA MAESTRO | IDM | MAESTRO emphasizes identity, delegation, and runtime control for autonomous workloads. |
| NIST AI RMF | AI RMF addresses governance and accountability for dynamic AI-driven access decisions. | |
| NIST CSF 2.0 | PR.AA | Authentication and access control are directly weakened by shared API tokens. |
Replace shared tokens with unique NHI credentials and enforce per-identity accountability.
