CAIP-25: JSON-RPC Provider Authorization

Author Pedro Gomes, Hassan Malik
Discussions-To https://github.com/ChainAgnostic/CAIPs/pull/25
Status Review
Type Standard
Created 2020-10-14
Updated 2022-10-26
Requires 2, 10, 171

Table of Contents

Simple Summary

CAIP-25 defines an authorization procedure for a chain agnostic provider to interface with a wallet as part of their initialization and/or “handshake” protocol.

Abstract

This proposal has the goal to define a standard procedure for decentralized applications to interface with chain agnostic cryptocurrency wallets and other user agents which govern identities (including accounts) in multiple cryptographic systems. It defines a lightweight protocol for negotiating and persisting authorizations during a session managed by a provider construct.

Motivation

The motivation comes from the lack of standardization across blockchains to expose accounts and define the expected JSON-RPC methods to be used by an application through a provider connecting to a signer or other user agent.

Specification

The session is proposed by a caller and the response by the respondent is used as the baseline for an ongoing session that both parties will persist. The properties and authorization scopes that make up the session are expected to be persisted and tracked over time by both parties in a discrete data store, identified by an entropic identifier assigned in the initial response. This object gets updated, extended, closed, etc. by successive calls and notifications, each tagged by this identifier.

If a respondent (e.g. a wallet) needs to initiate a new session, whether due to user input, security policy, or session expiry reasons, it can simply generate a new session identifier to signal this notification to the calling provider; if a caller needs to initiate a new session, it can do so by sending a new request without a sessionIdentifier. In such cases, a respondent (e.g. wallet) may choose to explicitly close all sessions upon generation of a new one from the same origin or identity, or leave it to time-out; maintaining concurrent sessions is discouraged (see Security Considerations).

Initial and ongoing authorization requests are grouped into two top-level arrays of scopeObjects, named requiredScopes and optionalScopes respectively. These two objects are not mutually exclusive (i.e., additional properties of a required scope may be requested in a separate scopeObject in the optional array, keyed to the same scope string). Note that scopeObjects can be keyed to a specific CAIP-2, or to a CAIP-104 namespace; if the latter defines a CAIP-2 profile, a scopes array MAY be set within it containing multiple CAIP-2 strings; this is functionally equivalent to defining multiple identical scopeObjects, each keyed to one of the CAIP-2s listed in the scopes array. See CAIP-217 for more details on the structure of the typed objects included in these arrays.

If any properties in the required scope(s) are not authorized by the respondent, a failure response expressive of one or more specific failure states will be sent (see #### failure states below), with the exception of user denying consent. For privacy reasons, an undefined response (or no response, depending on implementation) should be sent to prevent incentivizing unwanted requests and to minimize the surface for fingerprinting of public web traffic (See Privacy Considerations below).

Conversely, a succesful response will contain all the required properties and the provider’s choice of the optional properties expressed in a single unified scopeObject. In the case of identically-keyed scopeObjects appearing in both arrays in the request where properties from both are returned as authorized, the two scopes MUST be merged in the response (see examples below). However, respondents MUST NOT restructure scopes (e.g., by folding properties from a [CAIP2][]-keyed, chain-specific scope object into a CAIP-104-keyed, namespace-wide scope object) as this may introduce ambiguities (See Security Considerations below).

Request

The application would interface with a provider to authorize that provider with a given set of parameters by calling the following JSON-RPC request

Example:

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "provider_authorize",
  "params": {
    "requiredScopes": {
      "eip155": {
        "scopes": ["eip155:1", "eip155:137"],
        "methods": ["eth_sendTransaction", "eth_signTransaction", "eth_sign", "get_balance", "personal_sign"],
        "notifications": ["accountsChanged", "chainChanged"]
      },
      "eip155:10": {
        "methods": ["get_balance"],
        "notifications": ["accountsChanged", "chainChanged"]
      },
      "wallet": {
        "methods": ["wallet_getPermissions", "wallet_switchEthereumChain", "wallet_creds_store", "wallet_creds_verify", "wallet_creds_issue", "wallet_creds_present"],
        "notifications": []
      },
      "cosmos": {
        ...
      }
    },
    "optionalScopes":{
      "eip155:42161": {
        "methods": ["eth_sendTransaction", "eth_signTransaction", "get_balance", "personal_sign"],
        "notifications": ["accountsChanged", "chainChanged"]
    },
    "sessionProperties": {
      "expiry": "2022-12-24T17:07:31+00:00",
      "caip154-mandatory": "true"
    }         
  }
}

The JSON-RPC method is labeled as provider_authorize and its params object contains “requiredScopes” and/or “optionalScopes” objects populated with CAIP-217 “scope objects” keyed to CAIP-217 scope strings.

  • The requiredScopes array MUST contain 1 or more scopeObjects, if present.
  • The optionalScopes array MUST contain 1 or more scopeObjects, if present.

A third object is the sessionProperties object, all of whose properties MUST be interpreted as optional, since requesting applications cannot mandate session variables to providers. Because they are optional, providers MAY respond with all of the requested properties, or a subset of the session properties, or no sessionProperties object at all; they MAY even replace the values of the optional session properties with their own values. Wallets may also interpret values of sessionProperties in how it assigns values (for example, which accounts to expose) based on flags or properties defined here. The sessionProperties object MUST contain 1 or more properties if present.

Requesting applications are expected to persisted all of these returned properties in the session object identified by the sessionId. All properties in sessionProperties and their values MUST conform to definitions in CAIP-170, and MUST be ignored (rather than persisted) if they do not; similarly, nothing except valid CAIP-217 objects may be present in requiredScopes, optionalScopes, and sessionScopes arrays; all other array members should be dropped.

Response

The wallet can respond to this method with either a success result or an error message.

Success

The successful result contains one mandatory string (keyed as sessionId with a value conformant to CAIP-171) and two session objects, both mandatory and non-empty.

The first is called sessionScopes and contains 1 or more scopeObjects.

  • All required scopeObjects and all, none, or some of the optional scopeObjects (at the discretion of the provider) MUST be included if successful.
  • Unlike the request, each scope object MUST also contain an accounts array, containing 0 or more CAIP-10-conformant accounts authorized for the session and valid in that scope. Additional constraints on the accounts authorized for a given session MUST be applied conformant to the namespace’s CAIP-10 profile, if one has been specified.

A sessionProperties object MAY also be present, and its contents MAY correspond to the properties requested in the response or not (at the discretion of the provider).

An example of a successful response follows:

{
  "id": 1,
  "jsonrpc": "2.0",
  "result": {
    "sessionId": "0xdeadbeef",
    "sessionScopes": {
      "eip155": {
        "chains": ["eip155:1", "eip155:137"],
        "methods": ["eth_sendTransaction", "eth_signTransaction", "get_balance", "eth_sign", "personal_sign"]
        "notifications": ["accountsChanged", "chainChanged"],
        "accounts": ["eip155:1:0xab16a96d359ec26a11e2c2b3d8f8b8942d5bfcdb", "eip155:137:0xab16a96d359ec26a11e2c2b3d8f8b8942d5bfcdb"]
      },
      "eip155:10": {
        "methods": ["get_balance"],
        "notifications": ["accountsChanged", "chainChanged"],
        "accounts:" []
      },
      "eip155:42161": {
        "methods": ["personal_sign"],
        "notifications": ["accountsChanged", "chainChanged"],
        "accounts":["eip155:42161:0x0910e12C68d02B561a34569E1367c9AAb42bd810"]
      },
      "wallet": {
        "methods": ["wallet_getPermissions", "wallet_switchEthereumChain", "wallet_creds_store", "wallet_creds_verify", "wallet_creds_issue", "wallet_creds_present"],
        "notifications": []
      },
      "cosmos": {
        ...
      }
    },      
    "sessionProperties": {
      "expiry": "2022-11-31T17:07:31+00:00"          
    }
  }
}

Failure States

The response MUST NOT be a JSON-RPC success result in any of the following failure states.

Generic Failure Code

Unless the dapp is known to the wallet and trusted, the generic/undefined error response,

{
  "id": 1,
  "jsonrpc": "2.0",
  "error": {
    "code": 0,
    "message": "Unknown error"
  }
}

is RECOMMENDED for any of the following cases:

  • the user denies consent for exposing accounts that match the requested and approved chains,
  • the user denies consent for requested methods,
  • the user denies all requested or any required scope objects,
  • the wallet cannot support all requested or any required scope objects,
  • the requested chains are not supported by the wallet, or
  • the requested methods are not supported by the wallet
Trusted Failure Codes

More informative error messages MAY be sent in trusted-counterparty circumstances, although extending this trust too widely may contribute to widespread fingerprinting and analytics which corrode herd privacy (see Privacy Considerations below). The core error messages over trusted connections are as follows:

The valid error messages codes are the following:

  • Unknown error OR no scopes were authorized
    • code = 5000
    • message = “Unknown error with request”
  • When user disapproves accepting calls with the request methods
    • code = 5001
    • message = “User disapproved requested methods”
  • When user disapproves accepting calls with the request notifications
    • code = 5002
    • message = “User disapproved requested notifications”
  • When provider evaluates requested chains to not be supported
    • code = 5100
    • message = “Requested chains are not supported”
  • When provider evaluates requested methods to not be supported
    • code = 5101
    • message = “Requested methods are not supported”
  • When provider evaluates requested notifications to not be supported
    • code = 5102
    • message = “Requested notifications are not supported”
Trust-Agnostic Malformed Request Failure Codes

Regardless of caller trust level, the following error responses can reduce friction and user experience problems in the case of malformed requests.

  • When provider does not recognize one or more requested method(s)
    • code = 5201
    • message = “Unknown method(s) requested”
  • When provider does not recognize one or more requested notification(s)
    • code = 5202
    • message = “Unknown notification(s) requested”
  • When a badly-formed request includes a chainId mismatched to scope
    • code = 5203
    • message = “Scope/chain mismatch”
  • When a badly-formed request defines one chainId two ways
    • code = 5204
    • message = “ChainId defined in two different scopes”
  • Invalid Session Properties Object
    • code = 5300
    • message = “Invalid Session Properties requested”
  • Session Properties requested outside of Session Properties Object
    • code = 5301
    • message = “Session Properties can only be optional and global”

Note: respondents SHOULD to implement support for core RPC Documents per each supported namespace to avoid sending error messages 5201 and 5202 in cases where 0, 5101 or 5102 would be more appropriate. Failure to do so may leak versioning or feature-completeness information to a malicious or fingerprinting caller.

Security Considerations

The crucial security function of a shared session negotiated and maintained by a series of CAIP-25 calls is to reduce ambiguity in authorization. This requires a potentially counterintuitive structuring of the building-blocks of a Chain-Agnostic session into scopes at the “namespace-wide” (CAIP-104) or at the “chain-specific” (CAIP-2) level; for this reason, requests and responses are structures as arrays of objects keyed to these scopes, formatted either as a CAIP-104 scheme OR as a full CAIP-2. While internal systems are free to translate this object into other structures, preserving it in the CAIP-25 interface is crucial to the unambiguous communication between caller and respondent about what exact authorization is granted.

Privacy Considerations

One major risk in browser-based or HTTP-based communications is “fingerprinting risk”, i.e. the risk that public or intercepted traffic can be used to deanonymize browsers and/or wallets deductively based on response times, error codes, etc. To minimize this risk, and to minimize the data (including behavioral data) leaked by responses to potentially malicious CAIP-25 calls, respondents are recommended to ignore calls

  1. which the respondent explicitly does not authorize,
  2. which are rejected automatically or by policy, or
  3. which are rejected for unknown reasons.

“Ignoring” these calls means responding to all three in a way that is indistinguishable to a malicious caller or observer which might deduce information from differences in those responses (including the time taken to provide them). Effectively, this means allowing requests in all three cases to time out even if the end-user experience might be better served by differentiating them, particularly in complex multi-party architectures where parties on one side of this interface need to have a shared understanding of why a request did not receive a response. At scale, however, better user experiences in a single architecture or context can contribute to a systemic erosion of anonymity.

Given this “silent time out” behavior, the best strategy to ensure good user experience is not to request too many properties in the initial establishment of a session and to iteratively and incrementally expand session authorization over time. This also contributes to a more consentful experience overall and encourages progressive trust establishment across complex architectures with many distinct actors and agents.

Another design pattern that accomodates the “silent time out” behavior is minor updates to the session. For example, a caller sending a request identical to a previous request (or a previous response) except for a new session expiry further in the future could expect one of exactly three responses:

  1. An identical response to the previous request (meaning the session extension was denied);
  2. A response identical expect that it includes the new, extended session expiry; or,
  3. A silent time out (meaning the calling behavior was malformed in ways the respondent cannot understand, or the respondent choses not to make explicit how the request was malformed, or the end-user rejected them, or the request itself was in violation of policy).

Changelog

  • 2023-03-29: refactored out scopeObject syntax as separate CAIP-217, simplified
  • 2022-11-26: add mandatory indexing by session identifier (i.e. CAIP-171 requirement)
  • 2022-10-26: Addressed Berlin Gathering semantics issues and params syntax; consolidated variants across issues and forks post-Amsterdam Gathering
  • CAIP-2 - Chain ID Specification
  • CAIP-10 - Account ID Specification
  • CAIP-25 - JSON-RPC Provider Request
  • CAIP-171 - Session Identifier, i.e. syntax and usage of sessionIds
  • CAIP-217 - Authorization Scopes, i.e. syntax for scopeObjects

Copyright and related rights waived via CC0.

Citation

Please cite this document as:

Pedro Gomes, Hassan Malik, "CAIP-25: JSON-RPC Provider Authorization," Chain Agnostic Improvement Proposals, no. 25, October 2020. [Online serial]. Available: https://github.com/ChainAgnostic/CAIPs/blob/master/CAIPs/caip-25.md