§ Identity Hub

Specification Status: Draft

Latest Draft: identity.foundation/identity-hub/spec

Editors:
Daniel Buchner (Block)
Tobias Looker (Mattr)
Contributors:
Henry Tsai (Microsoft)
XinAn Xu (Microsoft)
Moe Jangda (Block)
Participate:
GitHub repo
File a bug
Commit history

§ Abstract

Most digital activities between people, organizations, devices, and other entities require the exchange of messages and data. For entities to exchange messages and data for credential, app, or service flows, they need an interface through which to store, discover, and fetch data related to the flows and experiences they are participating in. Identity Hubs are a data storage and message relay mechanism entities can use to locate public or private permissioned data related to a given Decentralized Identifier (DID). Identity Hubs are a mesh-like datastore construction that enable an entity to operate multiple instances that sync to the same state across one another, enabling the owning entity to secure, manage, and transact their data with others without reliance on location or provider-specific infrastructure, interfaces, or routing mechanisms.

§ Status of This Document

Identity Hub is a DRAFT specification under development within the Decentralized Identity Foundation (DIF). It incorporates requirements and learnings from related work of many active industry players into a shared specification that meets the collective needs of the community.

The specification will be updated to incorporate feedback, from DIF members and the wider community, with a reference implementation being developed within DIF that exercises the features and requirements defined here. We encourage reviewers to submit GitHub Issues as the means by which to communicate feedback and contributions.

§ Terminology

Identity Hub
A decentralized personal and application data storage and message relay node, as defined in the DIF Identity Hub specification.
Hub Instance
An instance of an Identity Hub running on a local device or at a remote location.
Hub Operator
Any entity, including individuals, who runs an Hub Instance on a device or infrastructure they control.
Hub User
An entity that stores DID-associated data and transmits messages via a given Hub Instance, which may be running on a device in their possession, or on the device or infrastructure of a Hub Operator.
Decentralized Identifiers
Unique ID URI string and PKI metadata document format for describing the cryptographic keys and other fundamental PKI values linked to a unique, user-controlled, self-sovereign identifier in a target system (e.g., blockchain, distributed ledger).

§ Topology

§ Protocol Stack

Identity Hubs are comprised of the following component layers, each of which is defined in this specification to ensure multiple Hub implementations can be used together and operate as a single logical unit for users.

DID Authentication
Access & Authorization
Interface Definitions
Interface Processing
Object Format
Object Signing / Encryption
File Structure
IPFS
TODO

Finalize the component stack list - are these correct? Are we missing any?

§ Service Endpoints

The following DID Document Service Endpoint entries MUST be present in the DID Document of a target DID for DID-relative URL resolution to properly locate the URI for addressing a DID owner’s Hub instances:

{
  "id": "did:example:123",
  "service": [{
    "id":"#hub",
    "type": "IdentityHub",
    "serviceEndpoint": {
      "instances": ["https://hub.example.com", "https://example.org/hub"]
    }
  }]
}

§ Addressing

A user’s logical Identity Hub (their collection of Hub Instances) can be addressed in many ways, but the mechanisms below MUST be supported by a compliant Identity Hub implementation:

§ DID-Relative URLs

The following DID URL constructions are used to address Hub Instances found to be associated with a given DID, as located via the DID resolution process.

§ Composition

The following process defines how a Identity Hub DID-Relative URL is composed:

  1. Let the base URI authority portion of the DID URL string be the target DID being addressed.
  2. Append a service parameter to the DID URL string with the value Identity Hub.
  3. Assemble an array of the Message Descriptor objects are desired for encoding in the DID-relative URL
  4. JSON stringify the array of Message Descriptor objects from Step 3, then Base64Url encode the stringified output.
  5. Append a queries parameter to the DID URL string with the value set to the JSON stringified, Base64Url encoded output of Step 4.

DID-relative URLs are composed of the following segments

did:example:123 + ?service=IdentityHub + &queries= + toBase64Url( JSON.stringify( [{ DESCRIPTOR_1 }, { DESCRIPTOR_N }] ) )

did:example:123?service=IdentityHub&queries=W3sgTUVTU0FHRV8xIH0sIHsgTUVTU0FHRV9OIH1d...

§ Resolution

The following process defines how a DID-Relative URL addressing an Identity Hub is resolved:

  1. Resolve the DID in the authority portion of the URL in accordance with the W3C Decentralized Identifier Resolution process, which returns the DID Document for the resolved DID.
  2. As indicated by the presence of the service parameter, locate the IdentityHub entry in the DID Document’s Service Endpoint entries.
  3. Parse the IdentityHub Service Endpoint object and select the first URI present in the serviceEndpoint objects instance array. NOTE: implementers SHOULD select from the URIs in the instance array in index order.
  4. If the URI located in step 3 is not a DID URI, proceed to step 5. If the URI from step 3 is a DID, resolve the DID and follow steps 2 and 3 to select the first URI in the DID’s IdentityHub Service Endpoint object instance array that is not a DID URI. Do not iterate this loop more than once - if a non-DID URI cannot be located after one loop of recursive resolution, terminate resolution and produce an error.
  5. Assuming a non-DID URI was located in steps 2-4, let the located URI be the base URI of the Hub request being constructed.

§ Request Construction

DID-Relative URL example for passing multiple messages:

NOTE

For example purposes, the queries parameter value below is neither JSON stringified nor Base64Url encoded, but should be when using Identity Hub URLs in practice (see the DID-relative URL Composition instructions above).

did:example:123?service=IdentityHub&queries=[{ "method": "CollectionsQuery", "schema": "https://schema.org/SocialMediaPosting" }]

did:example:123?service=IdentityHub&queries=W3sgTUVTU0FHRV8xIH0sIHsgTUVTU0FHRV9OIH1d...

Resolve DID to locate the Identity Hub URIs:

did:example:123 --> resolve to Identity Hub endpoint(s) --> https://hub.example.com/

Construct the Request Object:

  1. Create a JSON object for the request.
  2. The Request Object MUST include a id property, and its value MUST be an [RFC4122] UUID Version 4 string to identify the request.
  3. The Request Object MUST include a target property, and its value MUST be the Decentralized Identifier base URI of the DID-relative URL.
  4. The Request Object MUST include a messages property, and its value MUST be an array composed of Message objects that are generated by parsing the DID-relative URL’s queries parameter value as a JSON array and performing the following steps for each entry:
    1. Construct a Message object.
    2. Set the descriptor property of the Message object to the entry, ensuring it is a valid Message Descriptor object.
    3. Augment the Message object with any signing and authorization values required, as described in the Messages section.
    4. Append the object to the Request Object’s messages array.

HTTP POST example:

POST https://hub.example.com/

BODY {
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "target": "did:example:123",
  "messages": [
    {
      "descriptor": {
        "method": "CollectionsQuery",
        "schema": "https://schema.org/SocialMediaPosting"
      }
    },
    {...}
  ]
}

§ Request Objects

Request Objects are JSON object envelopes used to pass messages to Identity Hub instances.

{  // Request Object
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "target": "did:example:123",
  "messages": [  // Message Objects
    {...},
    {...},
    {...}
  ]
}

Request Objects are composed as follows:

  1. The Request Object MUST include a requestId property, and its value MUST be an [RFC4122] UUID Version 4 string to identify the request.
  2. The Request Object MUST include a target property, and its value MUST be the Decentralized Identifier base URI of the DID-relative URL.
  3. The Request Object MUST include a messages property, and its value MUST be an array composed of Message objects.

§ Messages

All Identity Hub messaging is transacted via Messages JSON objects. These objects contain message execution parameters, authorization material, authorization signatures, and signing/encryption information. For various purposes Messages rely on IPFS CIDs and DAG APIs.

{  // Request Object
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "target": "did:example:123",
  "messages": [  // Message Objects
    {
      "data": BASE64_STRING,
      "descriptor": {
        "method": INTERFACE_METHOD_STRING,
        "cid": DATA_CID_STRING,
        "dataFormat": DATA_FORMAT_STRING,
      },
      "attestation": {
        "protected": {
          "alg": "ES256K",
          "kid": "did:example:123#key-1"
        },
        "payload": CID(descriptor),
        "signature": Sign(protected + payload)
      },
      "authorization": {
        "protected": {
          "alg": "ES256K",
          "kid": "did:example:456#key-2",
          "capabilities": "...",
        },
        "payload": CID(descriptor),
        "signature": Sign(protected + payload)
      }
    },
    {...}
  ]
}

Messages objects MUST be composed as follows:

In order to enable data replication features for a Hub Instance, all Messages MUST be committed to an IPFS DAG in a tree allocated to the DID of the owner after all subtrees are composed and committed. The top-level of Message objects MUST be committed as a DAG CBOR encoded object.

§ Message Descriptors

The Identity Hub data structure that resides in the descriptor property of the Message is comprised of a common JSON structure that contains the following properties regardless of whether the message data is signed/encrypted:

{  // Request Object
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "target": "did:example:123",
  "messages": [  // Message Objects
    {
      "data": BASE64_STRING,
      "descriptor": {  // Message Descriptor
        "method": INTERFACE_METHOD_STRING,
        "cid": DATA_CID_STRING,
        "dataFormat": DATA_FORMAT_STRING,
      },
      "attestation": {...},
      "authorization": {...}
    },
    {...}
  ]
}

Message Descriptors are JSON objects that contains the parameters, signatory proof, and other details about the message and any data associated with it. All Message Descriptor objects share the following property options:

Individual Interface methods may describe additional properties that the descriptor object MUST or MAY contain, which are detailed in the Interfaces section of the specification.

§ Raw Data

If there is no need or desire to sign or encrypt the content of a message (i.e. public repudiable data), the message descriptor object is the only property required in a Message (with any method-specific properties required). An optional data property may be passed at the Message level that contains the data associated with the message (when data is desired or required to be present for a given method invocation).

{ // Message
  "data": BASE64_STRING,
  "descriptor": {
    "objectId": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
    "cid": CID(data),
    "dateCreated": 123456789,
    "method": "CollectionsWrite",
    "schema": "https://schema.org/SocialMediaPosting",
    "dataFormat": "application/json"
  }
}

§ Signed Data

If the object is to be attested by a signer (e.g the Hub owner via signature with their DID key), the object MUST contain the following additional properties to produce a [RFC7515] Flattened JSON Web Signature (JWS) object:

{ // Message
  "data": {...},
  "descriptor": {
    "objectId": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
    "cid": CID(data),
    "dateCreated": 123456789,
    "method": "CollectionsWrite",
    "schema": "https://schema.org/SocialMediaPosting",
    "dataFormat": "application/json"
  },
  "attestation": {
    "protected": {
      "alg": "ES256K",
      "kid": "did:example:123#key-1"
    },
    "payload": CID(descriptor),
    "signature": Sign(protected + payload)
  },
  ...
}

The message generating party MUST construct the signed message object as follows:

  1. If the Message includes associated data, passed directly via the Message object’s data property or through a channel external to the Message, add a cid property to the descriptor object and set its value as the stringified Version 1 CID of the DAG PB encoded data.
  2. The Message object MUST contain an attestation property, and its value MUST be a Flattened object representation of a [RFC7515] JSON Web Signature composed as follows:
  3. The Message object must include a payload property, and its value must be the stringified Version 1 CID of the DAG CBOR encoded descriptor object, whose composition is defined in the Message Descriptor section of this specification.
  4. The Message object MUST include a protected property, and its value must be an object composed of the following values:
    • The object MUST include an alg property, and its value MUST be the string representing the algorithm used to verify the signature (as defined by the [RFC7515] JSON Web Signature specification).
    • The object MUST include a kid property, and its value MUST be a DID URL string identifying the key to be used in verifying the signature.
  5. The Message object MUST include a signature property, and its value must be a signature string produced by signing the protected and payload values, in accordance with the [RFC7515] JSON Web Signature specification.

§ Encrypted Data

If the object is to be encrypted (e.g the Hub owner encrypting their data to keep it private), the descriptor object MUST be constructed as follows:

{ // Message
  "data": { 
    "protected": ...,
    "recipients": ...,
    "ciphertext": ...,
    "iv": ...,
    "tag": ... 
  },
  "descriptor": {
    "objectId": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
    "cid": CID(data),
    "dateCreated": 123456789,
    "method": "CollectionsWrite",
    "schema": "https://schema.org/SocialMediaPosting",
    "dataFormat": "application/json",
    "encryption": "jwe"
  },
  ...
}

The message generating party MUST construct an encrypted message as follows:

  1. The encryption property of the descriptor object MUST be set to the string value JWE.
  2. Generate an [RFC7516] JSON Web Encryption (JWE) object for the data that is to be represented in the message.
  3. Generate a Version 1 CID from the JWE of the data produced in Step 1, and set the cid property of the descriptor object as the stringified representation of the CID.

§ Signed & Encrypted Data

If the object is to be both attributed to a signer and encrypted encrypted, it MUST be structured as follows:

{ // Message
  "data": { 
    "protected": ...,
    "recipients": ...,
    "ciphertext": ...,
    "iv": ...,
    "tag": ... 
  },
  "descriptor": {
    "objectId": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
    "cid": CID(data),
    "dateCreated": 123456789,
    "method": "CollectionsWrite",
    "schema": "https://schema.org/SocialMediaPosting",
    "dataFormat": "application/json",
    "encryption": "jwe"
  },
  "attestation": {
    "protected": {
      "alg": "ES256K",
      "kid": "did:example:123#key-1"
    },
    "payload": CID(descriptor),
    "signature": Sign(protected + payload)
  }
}

The message generating party MUST construct the signed and encrypted message as follows:

  1. Follow the instructions described in the Encrypted Data section to add the required properties to the descriptor and produce a [RFC7516] JSON Web Encryption (JWE) object from the associated data.
  2. Follow the instructions described in the Signed Data section to add an attestation property with a Flattened object representation of a [RFC7515] JSON Web Signature as its value.

§ Response Objects

Responses from Interface method invocations are JSON objects that MUST be constructed as follows:

  1. The object MUST include an requestId property, and its value MUST be the [RFC4122] UUID Version 4 string from the requestId property of the Request Object it is in response to.
  2. The object MAY have a status property if an error is produced from a general request-related issue, and if present its value MUST be an object composed of the following properties:
    • The status object MUST have a code property, and its value MUST be an integer set to the HTTP Status Code appropriate for the status of the response.
    • The status object MAY have a message property, and if present its value MUST be a string that describes a terse summary of the status. It is recommended that the implementer set the message text to the standard title of the HTTP Status Code, when a title/message has already been defined for that code.
  3. The object MAY have a replies property, and if present its value MUST be an array of Message Result Objects, which are constructed as follows:
    1. The object MUST have a messageId property, and its value MUST be the stringified Version 1 CID of the associated message in the Request Object from which it was received.
    2. The object MUST have a status property, and its value MUST be an object composed of the following properties:
      • The status object MUST have a code property, and its value MUST be an integer set to the HTTP Status Code appropriate for the status of the response.
      • The status object MAY have a message property, and if present its value MUST be a string that describes a terse summary of the status. It is recommended that the implementer set the message text to the standard title of the HTTP Status Code, when a title/message has already been defined for that code.
    3. The object MAY have a entries property if the message request was successful. If present, its value MUST be the resulting message entries returned from the invocation of the corresponding message.

§ Request-Level Status Coding

If any of the scenarios described in this section are encountered during general message processing, the implementation must include a request-level status property, and its value must be an object as defined below.

Target DID not found

If the DID targeted by a request object is not found within the Hub instance, the implementation MUST produce a request-level status with the code 404, and SHOULD use Target DID not found within the Identity Hub instance as the status text.

Response Example:

EXAMPLE
{
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "status": {
    "code": 404,
    "text": "Target DID not found within the Identity Hub instance"
  }
}

General request-level processing errors

If a general request-level error in processing occurs that is not covered by one of the specific status cases above and prevent the implementation from correctly evaluating the request, the implementation MUST produce a request-level status with the code 500, and SHOULD use The request cannot not be processed as the status text.

Response Example:

EXAMPLE
{
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "status": {
    "code": 500,
    "text": "The request could not be processed correctly"
  }
}

§ Message-Level Status Coding

If any of the scenarios described in this section are encountered during the processing of an individual message, the implementation must include a message-level status property, and its value must be an object as defined below.

Message succeeded for query/read-type interface that expects results

If a message is processed correctly and a set of result entries is expected, the implementation MUST include a message-level status object with its code property set to 200, and SHOULD use The message was successfully processed as the status text.

NOTE

If no results are found, the status remains 200, and the implementation MUST return an empty entries array.

Request Example:

{  // Request Object
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "target": "did:example:123",
  "messages": [  // Message Objects
    {
      "descriptor": {
        "method": "CollectionsQuery",
        "schema": "https://schema.org/SocialMediaPosting"
      }
    },
    ...
  ]
}

Response Example:

EXAMPLE
{
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "replies": [
    {
      "messageId": "bm4vvfvsdfovsj...",
      "status": { "code": 200, "text": "OK" },
      "entries": [...]
    }
  ]
}

Improperly constructed message

If a message is malformed or constructed with invalid properties/values, the implementation MUST include a message-level status object with its code property set to 400, and SHOULD use The message was malformed or improperly constructed as the status text.

Request Example:

{  // Request Object
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "target": "did:example:123",
  "messages": [  // Message Objects
    {
      "descriptorization": {
        "methodical": "CollectionsQuery",
        "schemata": "https://schema.org/SocialMediaPosting"
      }
    }
  ]
}

Response Example:

EXAMPLE
{
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "replies": [
    {
      "messageId": "bm4vvfvsdfovsj...",
      "status": { "code": 400, "text": "The message was malformed or improperly constructed" }
    }
  ]
}

Message failed authorization requirements

If a message fails to meet authorization requirements during processing, the implementation MUST include a message-level status object with its code property set to 401, and SHOULD use The message failed authorization requirements as the status text.

Request Example:

{  // Request Object
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "target": "did:example:123",
  "messages": [  // Message Objects
    { // Message
      "data": {...},
      "descriptor": {
        "objectId": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
        "cid": CID(data),
        "dateCreated": 123456789,
        "method": "CollectionsWrite",
        "schema": "https://schema.org/SocialMediaPosting",
        "dataFormat": "application/json"
      }

      ^  `authorization` PROPERTY MISSING
    }
  ]
}

Response Example:

EXAMPLE
{
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "replies": [
    {
      "messageId": "bm2343w4vw45gh...",
      "status": { "code": 401, "text": "OK" }
    }
  ]
}

Interface is not implemented

If a message attempts to invoke an interface method that is not the implementation does not support, the implementation MUST include a message-level status object with its code property set to 501, and SHOULD use The interface method is not implemented as the status text.

Request Example:

{  // Request Object
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "target": "did:example:123",
  "messages": [  // Message Objects
    { // Message
      "data": {...},
      "descriptor": {
        "objectId": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
        "cid": CID(data),
        "method": "ThreadsCreate",
        "schema": "https://schema.org/LikeAction",
        "dataFormat": "application/json"
      }
    }
  ]
}

Response Example:

EXAMPLE
{
  "requestId": "c5784162-84af-4aab-aff5-f1f8438dfc3d",
  "replies": [
    {
      "messageId": "bm2343w4vw45gh...",
      "status": { "code": 501, "text": "The interface method is not implemented" }
    }
  ]
}

§ Access & Permissions

TODO

Agree on an access/permission scheme (e.g. Object Capabilities) for Hub interactions that require it.

§ Sync & Replication

TODO

IPFS can provide this to some extent, but do we need anything in addition to what native IPFS provides?

§ Interfaces

§ Feature Detection

The Identity Hub specification defines well-recognized Hub configurations to maximize interoperability (see Hub Configurations), but implementers may wish to support a custom subset of the Interfaces and features. The Feature Detection interface is the means by which a Hub expresses support for the Interfaces and features it implements.

§ Data Model

A compliant Identity Hub MUST produce a Feature Detection object defined as follows:

{
  "type": "FeatureDetection",
  "interfaces": { ... }
}
§ Properties & Values

The following properties and values are defined for the Feature Detection object:

§ Read

All compliant Hubs MUST respond with a valid Feature Detection object when receiving the following request object:

{ // Message
  "descriptor": { // Message Descriptor
    "method": "FeatureDetectionRead"
  }
}

§ Collections

To maximize decentralized app and service interoperability, the Collections interface of Identity Hubs provides a mechanism to store data relative to shared schemas. By storing data in accordance with a given schema, which may be well-known in a given vertical or industry, apps and services can leverage the same datasets across one another, enabling a cohesive, cross-platform, cross-device, cross-app experience for users.

§ Query

CollectionsQuery messages are JSON objects that include general Message Descriptor properties and the following additional properties, which must be composed as follows:

Get a single object by its ID reference:

{ // Message
  "descriptor": {
    "method": "CollectionsQuery",
    "objectId": "b6464162-84af-4aab-aff5-f1f8438dfc1e"
  }
}

Get a objects of a given schema type:

{ // Message
  "descriptor": {
    "method": "CollectionsQuery",
    "schema": "https://schema.org/MusicPlaylist"
  }
}

Get all objects of a given schema type:

{ // Message
  "descriptor": {
    "method": "CollectionsQuery",
    "dataFormat": "image/gif"
  }
}

§ Write

CollectionsWrite messages are JSON objects that include general Message Descriptor properties and the following additional properties, which must be composed as follows:

{ // Message
  "data": {...},
  "descriptor": { // Message Descriptor
    "objectId": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
    "cid": CID(data),
    "dateCreated": 123456789,
    "method": "CollectionsWrite",
    "schema": "https://schema.org/SocialMediaPosting",
    "dataFormat": DATA_FORMAT
  }
}
§ Processing Instructions

When processing a CollectionsWrite message, Hub instances MUST perform the following additional steps:

  1. If the incoming message has a higher dateCreated value than all of the other messages for the logical entry known to the Hub Instance, the message MUST be designated as the latest state of the logical entry and fully replace all previous messages for the entry.
  2. If the incoming message has a lower dateCreated value than the message that represents the current state of the logical entry, the message MUST NOT be applied to the logical entry and its data MAY be discarded.
  3. If the incoming message has a dateCreated value equal to the message that represents the current state of the logical entry, the incoming message’s IPFS CID and the IPFS CID of the message that represents the current state must be lexicographically compared and handled as follows:
    • If the incoming message has a higher lexicographic value than the message that represents the current state, perform the actions described in Step 1 of this instruction set.
    • If the incoming message has a lower lexicographic value than the message that represents the current state, perform the actions described in Step 2 of this instruction set.

§ Commit

{ // Message
  "data": {...},
  "descriptor": { // Message Descriptor
    "objectId": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
    "cid": CID(data),
    "dateCreated": 123456789,
    "method": "CollectionsCommit",
    "schema": "https://schema.org/SocialMediaPosting",
    "strategy": "merge-patch",
    "dataFormat": DATA_FORMAT
  }
}

CollectionsCommit messages are JSON objects that include general Message Descriptor properties and the following additional properties, which must be composed as follows:

§ Delete

{ // Message
  "descriptor": { // Message Descriptor
    "method": "CollectionsDelete",
    "objectId": "Qm65765jrn7be64v5q35v6we675br68jr"
  }
}

CollectionsDelete messages are JSON objects that include general Message Descriptor properties and the following additional properties, which must be composed as follows:

§ Threads

Threads are a linked series of topically associated messages that are intended to result in activities performed by entities participating in the message thread.

§ Query

{ // Message
  "descriptor": { // Message Descriptor
    "method": "ThreadsQuery",
    "schema": "https://schema.org/LikeAction"
  }
}

§ Create

{ // Message
  "data": {...},
  "descriptor": { // Message Descriptor
    "objectId": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
    "method": "ThreadsCreate",
    "schema": "https://schema.org/LikeAction"
  }
}

ThreadsCreate messages are JSON objects that include general Message Descriptor properties and the following additional properties, which must be composed as follows:

§ Reply

{ // Message
  "data": {...},
  "descriptor": { // Message Descriptor
    "objectId": "65efm7eg-84af-4aab-aff5-f1f8438dfc1e",
    "method": "ThreadsReply",
    "schema": "https://fintech.org/BidAcceptance",
    "root": "b6464162-84af-7gab-aff5-j8f8438dfc1e",
    "parent": "r7874162-84af-4aab-aff5-f1f8438dfc1e"
  }
}

ThreadsReply messages are JSON objects that include general Message Descriptor properties and the following additional properties, which must be composed as follows:

§ Close

{ // Message
  "descriptor": { // Message Descriptor
    "method": "ThreadsClose",
    "root": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
  }
}

ThreadsClose messages are JSON objects that include general Message Descriptor properties and the following additional properties, which must be composed as follows:

§ Delete

{ // Message
  "descriptor": { // Message Descriptor
    "method": "ThreadsDelete",
    "root": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
  }
}

ThreadsDelete messages are JSON objects that include general Message Descriptor properties and the following additional properties, which must be composed as follows:

§ Permissions

The Permissions interface provides a mechanism for external entities to request access to various data and functionality provided by an Identity Hub. Permissions employ a capabilities-based architecture that allows for DID-based authorization and delegation of authorized capabilities to others, if allowed by the Identity Hub owner.

§ Request

PermissionsRequest messages are JSON objects that include general Message Descriptor properties and the following additional properties, which must be composed as follows:

{
  "descriptor": {
    "method": "PermissionsRequest",
    "objectId": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
    "requester": "did:example:bob",
    "description": "Help you create and edit your music playlists",
    "ability": {
      "can": {
        "method": "CollectionsWrite",
        "schema": "https://schema.org/MusicPlaylist"
      },
      "conditions": {
        "encryption": 1,
        "attestation": 0,
        "delegation": true,
        "sharedAccess": true
      }
    }
  },
  "attestation": {
    "protected": {
      "alg": "ES256K",
      "kid": "did:example:bob#key-1"
    },
    "payload": CID(descriptor),
    "signature": Sign(protected + payload)
  }
}

§ Grant

PermissionsGrant messages are JSON objects that are generated either in response to evaluation of a PermissionsRequest message or optimistically by a user agent. PermissionsGrant messages include general Message Descriptor properties and the following additional properties, which must be composed as follows:

{
  "descriptor": {
    "method": "PermissionsGrant",
    "objectId": "f45wve-5b56v5w-5657b4e-56gqf35v",
    "grantedFor": "b6464162-84af-4aab-aff5-f1f8438dfc1e",
    "cid": "bf34455ev6v365eb7r8n9mnbesv5e6be7rn879m",
    "dataFormat": "application/json"
  },
  "data": {
    "payload": {
      "iss": "did:example:alice",
      "aud": "did:example:bob",
      "exp": 1575606941,
      "att": [{
        "can": {
          "method": "CollectionsWrite",
          "schema": "https://schema.org/MusicPlaylist",
        },
        "conditions": {
          "encryption": 1,
          "attestation": 0,
          "sharedAccess": true
        }
      }]
    },
    "signature": "fw547v63bo5687wvwbcqp349vwo876uc3q..."
  } 
}
§ Grantor PermissionsGrant Storage

After generating a PermissionsGrant the user agent (e.g. wallet app with access to authoritative keys for a given DID) MUST commit the granted permission object to the Hub of the DID the grant was issued from. This will ensure that the permission is present when addressed in subsequent interface method invocations.

§ Grantee PermissionsGrant Delivery

Once a user agent (e.g. wallet app with access to authoritative keys for a given DID) generates a PermissionsGrant for an entity to permit access to data and Hub functionality, it is the responsibility of the user agent that generated the PermissionsGrant to deliver it to the entity that is the subject. To do this, the user agent MUST generate a Request that includes the PermissionsGrant and send it to the Hub of the subject it has been granted to, in accordance with the Resolution and Request Construction sections of this specification.

§ Revoke

Revocation of a permission is the act of closing off any additional or invalid invocations of that permission. The Revoke interface method enables revocation of a permission via direct reference to the permission’s objectId. When executing a valid PermissionsRevoke invocation an implementation MUST use the inclusionProof value to ensure that only the entries in the Hub indicated by the proof are allowed to be retained in relation to the permission. The process of permission revocation effectively encapsulates all valid invocations of the permission and provides a deterministic means for ensuring no invalid invocations are allowed or persisted across any Hub instance.

{ // Message
  "descriptor": { // Message Descriptor
    "method": "PermissionsRevoke",
    "objectId": "Qm65765jrn7be64v5q35v6we675br68jr",
    "inclusionProof": "..." 
  }
}

§ Capability Objects

Capabilities granted via the Permissions interface are [RFC7516] JSON Web Token (JWT) used to secure and attenuate the scope permitted activities. The JWTs used in this specification to represent capabilities generally adhere to the JWT variant defined in the UCAN capability-based authorization construction.

Capability objects are JSON Web Tokens that must be composed as follows:

EXAMPLE
{
  "payload": {
    "iss": "did:example:alice",
    "aud": "did:example:bob",
    "nbf": 1529496683,
    "exp": 1575606941,
    "nnc": "f5we67hrn8676bwv5cq24WF5WVE6B76F",
    "att": [{
      "can": {
        "method": "CollectionsWrite",
        "schema": "https://schema.org/MusicPlaylist",
      },
      "conditions": {
        "encryption": 1,
        "attestation": 0,
        "sharedAccess": true
      }
    }],
    "prf": ["eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsInVhdiI6IjAuMS4wIn0.eyJhdWQiOiJkaWQ6a2V5OnpTdEVacHpTTXRUdDlrMnZzemd2Q3dGNGZMU..."]
  },
  "signature": "fw547v63bo5687wvwbcqp349vwo876uc3q..."
}

§ Commit Strategies

Some interface methods may be bound to, or allow for choice between, the data modification algorithms detailed below. Interfaces methods that are bound to one or more of these strategies will indicate it within their interface definitions under the Interfaces section.

§ Last-Write Wins

Last-Write Wins is the most basic Commit Strategy that allows for the traditional experience of posting an update to a file that fully replaces the data.

§ JSON Merge Patch

TODO

Detail JSON Merge Patch as a commit strategy option.

§ Hub Configurations

While it is strongly encouraged to implement the full set of Identity Hub features and Interfaces, not all devices and providers may be capable of doing so. To allow for maximum reach and proliferation in the ecosystem, the following are well-recognized configurations of Identity Hub feature sets that tend to serve different purposes.

§ Open Data Publication

This Hub configuration is ideal for implementers who seek to expose intentionally public data via the Identity Hub semantic data discovery Interfaces. This implementation is lightweight does not require the implementer to support any of the authentication, permissioning, or ingest mechanisms that other features and Interfaces do.

{
  "type": "FeatureDetection",
  "interfaces": {
    "collections": {
      "CollectionsQuery": true
    }
  }
}

§ Normative References

RFC4122
A Universally Unique IDentifier (UUID) URN Namespace. P. Leach; M. Mealling; R. Salz; 2005-07. Status: Proposed Standard.
RFC7515
JSON Web Signature (JWS). M. Jones; J. Bradley; N. Sakimura; 2015-05. Status: Proposed Standard.
RFC7516
JSON Web Encryption (JWE). M. Jones; J. Hildebrand; 2015-05. Status: Proposed Standard.
RFC7519
JSON Web Token (JWT). M. Jones; J. Bradley; N. Sakimura; 2015-05. Status: Proposed Standard.

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