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UCAN lets an application delegate specific authority to an AI agent without handing over the owner’s private signing key. It is a protocol and set of specifications—not a password replacement that works automatically with every account or agent. The service still needs to define and enforce what each permitted action means.
What UCAN delegation does
UCAN stands for User Controlled Authorization Network. Its principals are identified by decentralized identifiers (DIDs). A delegation is a signed authorization claim that identifies an issuer, audience, subject, command, policy, nonce and validity period. The issuer signs it with a private key; the recipient receives authority described by the claim, not the key that created the signature. The UCAN Delegation Specification v1.0.0 describes this as transferring authority without transferring cryptographic keys.
Think of a delegation as a limited work pass. It should identify the agent and resource, specify only the action required, constrain the policy or arguments where the application supports that, and expire when the work should no longer be authorized. Unlike a password, a UCAN delegation is scoped authorization—but it only helps where the target service has implemented UCAN-aware authorization.
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Capabilities name the allowed action
A capability associates a resource or subject with a command and policy. Command paths can be hierarchical, so a grant to a broader path can cover its descendants. The / wildcard is especially powerful: it can cover all capabilities for a resource. Avoid broad grants when a specific command will do.
Delegation chains can narrow authority, not expand it
An agent may delegate authority onward, but each direct delegation must restate or attenuate the capabilities granted by its delegator. A downstream recipient cannot legitimately receive more authority through that chain than the delegator held. The application must define what counts as a valid child resource or narrower ability; those semantics are not universal across services.
The UCAN Specification sets out the high-level model and security considerations. The delegation specification defines the delegation claim and its fields.
What UCAN does not guarantee
A valid signature chain does not make an operation safe
Cryptographic verification establishes that the delegations were signed and linked as required; it does not establish that a requested operation is meaningful, safe or directed at the right resource. At execution time, the service must verify resource ownership and interpret the command according to that resource’s rules. If an integration wraps a service that still relies on ambient access-control lists (ACLs), some authorization remains outside UCAN, increasing the security surface and weakening the guarantees.
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UCAN includes revocation, but it does not provide complete confinement. A delegate may subdelegate without notifying the original issuer. The UCAN Specification explains that UCANs “do not offer confinement” because guaranteeing knowledge of all sub-delegations would require all processes to be online. Treat revocation as one control in an authorization design, not proof that every downstream grant has been found or neutralized.
Authentication and replay checks remain necessary
The specification does not claim special protection against person-in-the-middle attacks. It recommends delegating only to trusted, authenticated agents over secure channels and checking that the topmost issuer is the expected DID. For invocation replay protection, it says each invocation must have a unique CID and the executor must check uniqueness against a local store of unexpired UCAN hashes.
How to apply UCAN safely to an agent task
- Identify the resource and agent. Confirm the resource the agent needs to act on and authenticate the intended agent. Verify that the delegation’s topmost issuer is the DID you expect.
- Grant only the required capability. Name the narrowest resource and command that accomplish the task. Avoid
/or similarly broad authority; constrain policy or arguments when the application supports it. - Set a short validity period. The delegation includes an expiration. Keep the grant valid only as long as the work requires, following the specification’s least-authority guidance.
- Keep signing keys in their original context. Do not send the owner’s private key to the agent. Use distinct keys for distinct physical devices and use cases to limit the consequences if one key is exposed.
- Enforce the capability at execution time. The service should validate the proof chain, confirm resource ownership, interpret the command for that resource and apply any required replay checks. A token alone cannot supply these application-specific checks.
- Review downstream delegation and revocation behavior. Decide whether subdelegation is permitted and how revocation works in the integration. Do not assume the original issuer automatically learns about every downstream grant.
Choosing a UCAN implementation
The UCAN Working Group’s project directory lists TypeScript, Rust, Go and Haskell implementations, alongside the core specifications. It presents the token and capabilities format as a starting point, with delegation, invocation, revocation and promises among the core specifications. The directory labels the HTTP bearer-token specification as outdated relative to v1, so check the current directory and the specific library’s status before building against it.
There is no source-supported basis here for ranking the listed libraries by performance or feature completeness. Choose based on the application’s language and runtime, support for the current v1 specifications, maintenance and compatibility, and whether the library’s delegation semantics fit the application’s resource model.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsThe TypeScript implementation illustrates that fit: an application configures functions that decide whether a child resource or ability may be delegated from its parent. Those rules determine whether a proposed attenuation is valid. UCAN support is not established for any particular AI-agent platform by the specifications alone; confirm that the agent and target service implement compatible authorization behavior before relying on it.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When UCAN is a good fit
UCAN is relevant when a system needs cryptographically verifiable, scoped authority that can be delegated without moving the signing key, and the application can define and enforce resource-specific capabilities. It is not a drop-in mechanism for giving any agent secure access to an existing account. The core specifications describe no measured reduction in agent credential breaches or other quantified security outcome; the benefits depend on the integration’s scope, enforcement and operational controls.
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