Credential Models

A detailed look at the different types of verifiable credentials used in MCP-I

Credential Models

Credential Flexibility

MCP-I supports multiple credential models to accommodate different security requirements, use cases, and enterprise needs while maintaining core verification principles.

Overview of Credentials in MCP-I

MCP-I uses W3C Verifiable Credentials (VCs) as the standard format for expressing claims about identity and delegation. The specification defines several credential models to address different requirements:

Standard Delegation Credential: The core credential type for basic delegation
Chained Delegation Credential: For multi-level delegation scenarios
Enhanced Credential: For Level 3 implementations with additional security features
Legacy Compatibility Credential: For interoperability with existing systems

Each model shares core properties while adding specific features for its intended use case.

Standard Delegation Credential

The Standard Delegation Credential is the foundation of MCP-I's delegation model, representing a direct authorization from a principal to an agent.

Structure

{
  "@context": [
    "https://www.w3.org/2018/credentials/v1",
    "https://mcp-i.org/credentials/v1"
  ],
  "id": "urn:uuid:3978344f-8596-4c3a-a978-8fcaba3903c5",
  "type": ["VerifiableCredential", "DelegationCredential"],
  "issuer": "did:example:principal123",
  "issuanceDate": "2025-01-01T19:23:24Z",
  "expirationDate": "2025-12-31T23:59:59Z",
  "credentialSubject": {
    "id": "did:example:agent456",
    "scope": ["read:data", "write:calendar"],
    "constraints": {
      "environment": "production"
    }
  },
  "credentialStatus": {
    "id": "https://example.com/status/123",
    "type": "StatusList2021Entry",
    "statusPurpose": "revocation",
    "statusListIndex": "94"
  },
  "proof": {
    "type": "Ed25519Signature2020",
    "created": "2025-01-01T19:23:24Z",
    "verificationMethod": "did:example:principal123#key-1",
    "proofPurpose": "assertionMethod",
    "proofValue": "z43BsK5Fu9Sdw7tF1JwPnBtYu..."
  }
}

Key Properties

id: Unique identifier for the credential (optional but recommended)
type: Must include both "VerifiableCredential" and "DelegationCredential"
scope: Array of permissions following the action:resource format
constraints: Optional conditions that further restrict the delegation

Standard Model Usage

The Standard Delegation Credential is suitable for most MCP-I implementations and is the minimum requirement for Level 1 conformance.

Chained Delegation Credential

The Chained Delegation Credential model supports scenarios where delegation flows through multiple entities. This model is essential for complex workflows where intermediary agents need to further delegate authority.

Structure

{
  "@context": [
    "https://www.w3.org/2018/credentials/v1",
    "https://mcp-i.org/credentials/v1"
  ],
  "id": "urn:uuid:9b37c28d-a7c2-4e5f-8d9a-1b2c3d4e5f6a",
  "type": ["VerifiableCredential", "ChainedDelegationCredential"],
  "issuer": "did:example:agentA",
  "issuanceDate": "2025-02-15T10:15:30Z",
  "expirationDate": "2025-06-30T23:59:59Z",
  "credentialSubject": {
    "id": "did:example:agentB",
    "scope": ["read:data"],
    "constraints": {
      "environment": "testing"
    }
  },
  "credentialStatus": {
    "id": "https://example.com/status/456",
    "type": "StatusList2021Entry",
    "statusPurpose": "revocation",
    "statusListIndex": "42"
  },
  "parentCredential": {
    "id": "urn:uuid:3978344f-8596-4c3a-a978-8fcaba3903c5",
    "type": ["VerifiableCredential", "DelegationCredential"],
    "issuer": "did:example:principal123",
    "issuanceDate": "2025-01-01T19:23:24Z",
    "expirationDate": "2025-12-31T23:59:59Z",
    "credentialSubject": {
      "id": "did:example:agentA",
      "scope": ["read:data", "write:calendar"]
    },
    "proof": {
      "type": "Ed25519Signature2020",
      "verificationMethod": "did:example:principal123#key-1",
      "proofValue": "z43BsK5Fu9Sdw7tF1JwPnBtYu..."
    }
  },
  "proof": {
    "type": "Ed25519Signature2020",
    "created": "2025-02-15T10:15:30Z",
    "verificationMethod": "did:example:agentA#key-1",
    "proofPurpose": "assertionMethod",
    "proofValue": "z82Kn2d7a9FjHnPoQ5..."
  }
}

Key Properties

type: Includes "ChainedDelegationCredential" to indicate delegation chain
parentCredential: The credential that authorizes the issuer to delegate
scope: Must be a subset of the parent credential's scope

Validation Requirements

When verifying a chained delegation, the entire chain must be validated recursively, ensuring each delegation's scope is a proper subset of its parent and no credential in the chain is expired or revoked.

Enhanced Credential

For Level 3 implementations, MCP-I defines the Enhanced Credential model with additional security and privacy features.

Structure

{
  "@context": [
    "https://www.w3.org/2018/credentials/v1",
    "https://mcp-i.org/credentials/v1",
    "https://w3id.org/security/bbs/v1"
  ],
  "id": "urn:uuid:5f1c8a2e-3d7b-4c6a-9f2d-8e7b6c5d4e3f",
  "type": ["VerifiableCredential", "EnhancedDelegationCredential"],
  "issuer": "did:example:principal123",
  "issuanceDate": "2025-03-10T08:30:15Z",
  "expirationDate": "2025-09-10T23:59:59Z",
  "credentialSubject": {
    "id": "did:example:agent789",
    "scope": ["read:data", "write:calendar", "admin:settings"],
    "constraints": {
      "environment": "production",
      "networkSegment": "internal",
      "geoFence": {
        "type": "Polygon",
        "coordinates": [[[longitude, latitude], ... ]]
      },
      "timeWindow": {
        "daysOfWeek": [1, 2, 3, 4, 5],
        "hoursOfDay": [8, 17]
      }
    }
  },
  "credentialStatus": {
    "id": "https://example.com/status/789",
    "type": "StatusList2021Entry",
    "statusPurpose": "revocation",
    "statusListIndex": "128"
  },
  "termsOfUse": [
    {
      "type": "DelegationPolicy",
      "prohibition": [
        {
          "purpose": ["Marketing", "DataSelling"]
        }
      ]
    }
  ],
  "auditTrail": {
    "hash": "sha256-8a9d8edf2175b0f2641a94d7as87f2afd847a",
    "logUrl": "https://audit.example.com/logs/credential789"
  },
  "proof": {
    "type": "BbsBlsSignature2020",
    "created": "2025-03-10T08:30:15Z",
    "verificationMethod": "did:example:principal123#key-2",
    "proofPurpose": "assertionMethod",
    "proofValue": "kTJVP7+H8z7F..."
  }
}

Key Features

Advanced Constraint Models: Supports complex constraints like geofencing and time windows
Terms of Use: Explicit delegation policies
Selective Disclosure Proofs: Using BBS+ signatures for zero-knowledge proofs
Audit Trail: Explicit links to immutable audit logs
Enhanced Crypto: Support for advanced cryptographic suites

Enterprise Integration

The Enhanced Credential model is particularly well-suited for enterprise environments with complex security policies, regulatory requirements, and integration with existing IAM systems.

Legacy Compatibility Credential

To facilitate integration with existing identity systems, MCP-I provides a Legacy Compatibility Credential model for Level 1 implementations.

Structure

{
  "@context": [
    "https://www.w3.org/2018/credentials/v1",
    "https://mcp-i.org/credentials/v1"
  ],
  "id": "urn:uuid:1a2b3c4d-5e6f-7g8h-9i0j-1k2l3m4n5o6p",
  "type": ["VerifiableCredential", "LegacyDelegationCredential"],
  "issuer": "did:example:idp456",
  "issuanceDate": "2025-04-20T14:25:10Z",
  "expirationDate": "2025-05-20T23:59:59Z",
  "credentialSubject": {
    "id": "did:example:agent101112",
    "scope": ["read:profile", "read:email"],
    "legacyIdentifier": {
      "type": "OAuth2Subject",
      "value": "user123@example.com",
      "issuer": "https://auth.example.com"
    }
  },
  "mappings": {
    "oauth": {
      "clientId": "client123",
      "scopes": ["profile", "email.read"]
    }
  },
  "proof": {
    "type": "Ed25519Signature2020",
    "created": "2025-04-20T14:25:10Z",
    "verificationMethod": "did:example:idp456#key-1",
    "proofPurpose": "assertionMethod",
    "proofValue": "zWaF5d8w93jWm..."
  }
}

Key Features

Legacy Identifier: Maps to existing identity systems like OAuth, OIDC, or LDAP
Mappings: Explicit mappings between MCP-I scopes and legacy authorization models
Limited Lifetime: Typically shorter expiration to manage security risk

Security Considerations

Legacy Compatibility Credentials offer reduced security guarantees compared to standard MCP-I credentials and should only be used during transition periods or for Level 1 implementations. Plan to migrate to full DID-based credentials for Level 2 and 3 conformance.

Credential Format Registry

MCP-I maintains a registry of recognized credential formats at https://knowthat.ai/registry/credential-types. When creating credentials, reference this registry for the latest context definitions and type identifiers.

The registry includes:

Canonical context URLs
Registered credential types
Required and optional fields for each type
Approved cryptographic suites

Credential Selection Guidelines

When choosing a credential model for your implementation, consider:

Credential Type	Use Case	Conformance Level	Security Level
Standard Delegation	Direct agent authorization	Level 1+	Moderate to High
Chained Delegation	Multi-level delegation	Level 2+	Moderate to High
Enhanced	Complex enterprise scenarios	Level 3	Very High
Legacy Compatibility	Integration with existing systems	Level 1 only	Basic

Implementation Flexibility

MCP-I allows for custom credential models as long as they include all required fields and can be verified according to the MCP-I verification protocol. Custom models should be registered with the credential registry for broader interoperability.

Implementation Examples

Creating a Standard Delegation Credential

import { createCredential } from "@mcp-i/credentials";

// Example function to create a standard delegation credential
async function createStandardDelegation(issuerDid, agentDid, scopes) {
  return await createCredential({
    type: "DelegationCredential",
    issuer: issuerDid,
    subject: agentDid,
    scope: scopes,
    expiresIn: "90d", // 90 days
    constraints: {
      environment: "production",
    },
  });
}

// Usage
const credential = await createStandardDelegation(
  "did:web:issuer.example.com",
  "did:key:z6MkhaSG3...",
  ["read:email", "write:calendar"]
);

Creating a Chained Delegation

import { createChainedDelegation } from "@mcp-i/credentials";

// Example function to create a chained delegation
async function delegateToSubAgent(parentCredential, subAgentDid, subsetScopes) {
  return await createChainedDelegation({
    parentCredential,
    subject: subAgentDid,
    scope: subsetScopes,
    expiresIn: "30d", // Must be <= parent expiration
  });
}

// Usage
const chainedCredential = await delegateToSubAgent(
  originalCredential,
  "did:key:z6MkhZgT8...",
  ["read:email"] // Subset of parent scopes
);

Next Steps

Explore the Delegation Flow to understand how these credentials are created and exchanged
Learn about Verification Protocol to see how different credential types are verified

Get Started

Concepts

Implementation

Credential Models

Credential Models

Credential Flexibility

Overview of Credentials in MCP-I

Standard Delegation Credential

Structure

Key Properties

Standard Model Usage

Chained Delegation Credential

Structure

Key Properties

Validation Requirements

Enhanced Credential

Structure

Key Features

Enterprise Integration

Legacy Compatibility Credential

Structure

Key Features

Security Considerations

Credential Format Registry

Credential Selection Guidelines

Implementation Flexibility

Implementation Examples

Creating a Standard Delegation Credential

Creating a Chained Delegation

Next Steps

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