AI Governance Engineer
GitHub

Token passthrough

By Updated

The anti-pattern in which a server accepts a token that was not issued to it and forwards it, unmodified, to a downstream API, which may then trust it as if the server had validated it. The MCP specification forbids it: a server must not accept any token not explicitly issued for it, and so checks each token's audience 1.

Developed in
ch. 23, MCP authorization as of 2026-07-28
Chapters
ch. 23, AI Agents
Contrast with
Delegation (OAuth token exchange)
Source
1 numbered reference, listed below

Where it is used

One chapter of the Body of Knowledge uses the term. Each link opens the first section that does.

Token passthrough: mentions per chapter3 mentions of the term across 1 of the 23 chapters of the Body of Knowledge; the chapters the glossary cross-references are drawn solid.Cross-referenced chapter23 AI Agents: 3 mentions23 AI Agents3No mentions in the other 22 chaptersSource: the Body of Knowledgev0.5.0
Token passthrough: mentions per chapter3 mentions of the term across 1 of the 23 chapters of the Body of Knowledge; the chapters the glossary cross-references are drawn solid.Cross-referenced chapter0001020304050607081011121314151617181920212223 AI Agents: 3 mentions323Source: the Body of Knowledge v0.5.0
Mentions per chapter How often each chapter names the term, with the chapters the glossary cross-references drawn solid. The longest bar is where to read the term in use; bars spread across many chapters mark a term that runs through the discipline.
Mentions as a table
Mentions of Token passthrough per chapter
ChapterMentionsCross-referenced
00 Preface0No
01 Definition0No
02 Why Now0No
03 Values & Principles0No
04 The Stack0No
05 Patterns0No
06 The Role0No
07 Maturity Model0No
08 Regulatory Map0No
10 Reading List0No
11 AI Defined0No
12 Governance Program0No
13 Risk Management0No
14 Development0No
15 Deployment0No
16 Fairness & XAI0No
17 Incidents0No
18 EU AI Act0No
19 Privacy & AI0No
20 Existing Law0No
21 AI Laws Worldwide0No
22 Principles & Standards0No
23 AI Agents3Yes
Token passthrough: related terms and patternsThe term at the centre; related terms on solid edges, the terms it is contrasted with on dashed edges, and the patterns that use it most in the colour of their layer.RelatedContrastToken passthroughRelated terms (2)CIMD · RelatedCIMDMCP · RelatedMCPContrast with (1)Delegation (OAuth token exchange) · ContrastDelegation
Token passthrough: related terms and patternsThe term at the centre; related terms on solid edges, the terms it is contrasted with on dashed edges, and the patterns that use it most in the colour of their layer.RelatedContrastRelated terms (2)CIMD · RelatedCIMDMCP · RelatedMCPContrast with (1)Delegation (OAuth token exchange) · ContrastDelegationTokenpassthrough
The term's neighbourhood Terms related to this one on solid edges, terms it is often confused with on dashed edges, and the patterns that use it most in the colour of their layer. Follow a dashed edge to check the distinction before you use either term.
Neighbourhood as a table
Neighbourhood of Token passthrough
FamilyItemRelation
Related termsCIMDRelated
Related termsMCPRelated
Contrast withDelegation (OAuth token exchange)Contrast
  • CIMD

    Client ID Metadata Document: the mechanism by which an OAuth client identifies itself with a URL, used as its client ID, that points to its metadata document.

  • MCP

    Model Context Protocol: an open protocol for connecting AI applications to tools and data sources; its 2026 specification adds OAuth 2.1 resource-server…

Sources

  1. [1] Model Context Protocol, Security Best Practices, version 2026-07-28 (token passthrough defined and explicitly forbidden; servers MUST NOT accept any tokens not explicitly issued for them; audience validation). Model Context Protocol. 2026-07-28. https://modelcontextprotocol.io/docs/2026-07-28/tutorials/security/security_best_practices (verified: primary)

Definitions of legal terms paraphrase the cited text, which governs. Dated statements are as of .

Cite this term

García Aibar, J. (2026). Token passthrough. In AI Governance Engineering: The Thesis & Body of Knowledge (v0.5.0), Glossary. https://doi.org/10.5281/zenodo.22956197. https://aigovernanceengineer.com/glossary/token-passthrough. CC BY 4.0

BibTeX

@misc{aige2026tokenpassthrough,
  author  = {Jorge García Aibar},
  title   = {{Token passthrough}},
  note    = {Glossary, AI Governance Engineering: The Thesis \& Body of Knowledge, version 0.5.0},
  year    = {2026},
  doi     = {10.5281/zenodo.22956197},
  url     = {https://aigovernanceengineer.com/glossary/token-passthrough}
}