[EN] Open Finance Brasil Financial-grade API Dynamic Client Registration 1.0 Implementers Draft 3

Foreword

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The Open Finance Brasil Initial Structure is responsible for creating standards and specifications necessary to meet the requirements and obligations of the Brasil Open Finance Legislation as originally outlined by the Brasil Central Bank. There is a possibility that some of the elements of this document may be the subject to patent rights. OFBIS shall not be held responsible for identifying any or all such patent rights.

Open Finance Brasil Financial-grade API Security Profile 1.0 consists of the following parts:

• Open Finance Brasil Financial-grade API Security Profile 1.0

• Open Finance Brasil Dynamic Client Registration Profile 1.0

These parts are intended to be used with RFC6749, RFC6750, RFC7636, OIDC, OIDR, RFC7591, RFC7592, FAPI-1-Baseline and FAPI-1-Advanced

Introduction

The Open Finance Brasil Financial-grade API Dynamic Client Registration Profile is a profile of RFC7591, RFC7592 and OIDR that aims to provide specific implementation guidelines for security and interoperability which can be applied to the identification, registration and management of OAuth Clients operating in the Brasil Open Finance ecosystem.

Although it is possible to code an OpenID Provider and Relying Party from scratch using this specification, the main audience for this specification are parties who already have a certified implementation of OpenID Connect and seek to obtain certification for the Brasil Open Finance programme.

Notational Conventions

The key words "shall", "shall not", "should", "should not", "may", and "can" in this document are to be interpreted as described in ISO Directive Part 2. These key words are not to be used as lexicon terms such that any occurrence of them shall be interpreted as key words and are not to be interpreted with their natural language meanings.

1. Scope

This document specifies the method of

• applications registered in the Open Finance Directory of Participants to discover OpenID Providers offering services in the Open Finance Brasil ecosystem;

• applications to use OpenID Connect Registration to onboard their applications with Bank OpenID Providers; and

• applications to use OAuth 2.0 Dynamic Client Registration Management Protocol to manage their applications with OpenID Providers;

This document is applicable to all participants engaging in Open Finance in Brasil.

2. Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applied. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISODIR2 - ISO/IEC Directives Part 2

RFC6749 - The OAuth 2.0 Authorization Framework

RFC6750 - The OAuth 2.0 Authorization Framework: Bearer Token Usage

RFC7636 - Proof Key for Code Exchange by OAuth Public Clients

RFC6819 - OAuth 2.0 Threat Model and Security Considerations

RFC7519 - JSON Web Token (JWT)

RFC7591 - OAuth 2.0 Dynamic Client Registration Protocol

RFC7592 - OAuth 2.0 Dynamic Client Registration Management Protocol

BCP195 - Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)

OIDC - OpenID Connect Core 1.0 incorporating errata set 1

FAPI-CIBA - Financial-grade API: Client Initiated Backchannel Authentication Profile

RFC4514 - Lightweight Directory Access Protocol (LDAP): String Representation of Distinguished Names

RFC4517 - Lightweight Directory Access Protocol (LDAP): Syntaxes and Matching Rules

OIDD - OpenID Connect Discovery 1.0 incorporating errata set 1

OIDR - OpenID Connect Registration 1.0 incorporating errata set 1

RFC8705 - OAuth 2.0 Mutual TLS Client Authentication and Certificate Bound Access Tokens

PAR - OAuth 2.0 Pushed Authorization Requests

JAR - OAuth 2.0 JWT Secured Authorization Request

FAPI-1-Baseline - Financial-grade API Security Profile 1.0 - Part 1: Baseline

FAPI-1-Advanced - Financial-grade API Security Profile 1.0 - Part 2: Advanced

OFB-FAPI - Open Finance Brasil Financial-grade API Security Profile 1.0

OFB-Cert-Standards - Open Finance Brasil x.509 Certificate Standards

OFB-DCR/DCM-Swagger - DCR & DCM Swagger

3. Terms and definitions

For the purpose of this document, the terms defined in RFC6749, RFC6750, RFC7636, OpenID Connect Core and ISO29100 apply.

4. Symbols and Abbreviated terms

• API - Application Programming Interface

• DCR - Dynamic Client Registration

• FAPI - Financial-grade API

• HTTP - Hyper Text Transfer Protocol

• OIDF - OpenID Foundation

• REST - Representational State Transfer

• SS - Software Statement

• SSA - Software Statement Assertion

• TLS - Transport Layer Security

5. Introduction

Brasil Open Finance ecosystem leverages a federation trust provider or directory of participants as the golden source of information on accredited participants and software that are authorized to partake in the Open Finance Brasil ecosystem.

The services by the Directory include

• Software registration and management.

• Software credential registration and management using ICP Certificates.

• Software Statement Assertion (SSA) generation

Participants within the ecosystem must leverage these services to facilitate API driven OAuth client registration using the process outlined in clause 3.1.1 of RFC7591 with additional metadata necessary to support OpenID Connect defined in OpenID Connect Registration.

It's important to remember that the client registration payload has most of its attributes as non-mandatory, and that assigned values that conflict with those in the software statement assertion will be overridden by the values of the software statement assertion issued by the Directory of Participants. Not all metadata a client wishes to provide may be contained in a software statement, e.g alternative Metadata Languages and Script values. There are some cases where the client metadata are subset of the existing values in the SSA, such as redirect_URIs.

6. Open Finance Brasil OpenID Connect Discovery provisions

6.1. Authorization server

The Authorization Server shall support OpenID Connect Discovery as required by Financial-grade API Security Profile 1.0 - Part 1: Baseline. This support shall be explicit in Participant Directory configurations, and in the declaration of its attributes in the Discovery file (well-known), respecting the authentication mechanisms certified by the institution through the Open Finance Brazil compliance tests.

In addition, the Authorization Server:

1. shall advertise its presence in the Open Finance Brasil ecosystem by being listed on the Directory of Participants;

2. shall advertise all Open Finance Brasil REST API resources protected by the OpenID Provider on the Directory of Participants;

3. shall advertise support for all signing, encryption, authentication mechanisms and standards required to support Open Finance Brasil Financial API;

4. shall advertise support for OpenID Dynamic Client Registration;

5. may advertise mtls_endpoint_aliases as per clause 5 RFC 8705 OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens the token_endpoint, registration_endpoint, userinfo_endpoint and push_authorization_request_endpoint;

6. if supporting Financial API - Client Initiated Back Channel Authentication shall advertise through OIDD mtls_endpoint_aliases the backchannel_authentication_endpoint;

7. shall not rotate the registration_access_token.

6.2. Client

The Client shall support OpenID Connect Discovery as required by Financial-grade API Security Profile 1.0 - Part 1: Baseline

In addition, the Client

1. shall rely on ecosystem discovery services provided by Directory of Participants only;

2. shall derive necessary Authorisation Server metadata by relying on an Authorization Servers OpenID Connect Discovery services only;

3. where present, shall use endpoints advertised in mtls_endpoint_aliases as per clause 5 RFC 8705 OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens;

7. Open Finance Brasil OpenID Connect Registration Provisions

7.1. Authorization server

The Authorization Server shall support the RFC RFCs Dynamic Client Registration (DCR) RFC7591, Dynamic Client Management (DCM) RFC7592 and OpenID Registration

In addition, the Authorization Server

1. shall reject dynamic client registration requests not performed over a connection secured with mutual tls using certificates issued by Brazil ICP (production) or the Directory of Participants (sandbox);

2. shall validate that the request contains software_statement JWT signed using the PS256 algorithim issued by the Open Finance Brasil directory of participants;

3. shall validate that the software_statement was issued (iat) not more than 5 minutes prior to the request being received;

4. shall validate that the attribute jwks (key set by value) was not included; but declared as a reference in the jwks_uri attribute;

5. shall, when informed, validate that jwks_uri matches the software_jwks_uri provided in the software_statement;

   1. shall validate if the content obtained through jwks_uri contains a certificate of type use: “enc”;

6. shall require and validate that redirect_uris matches or contains a sub set of software_redirect_uris provided in the software_statement;

7. shall require and validate that all client authentication mechanism adhere to the requirements defined in RFC7591 and RFC7592, validating the registration_access_token and, through a secure connection, the certificate chain of ICP-Brasil;

8. removed;

9. shall validate that the requested scopes are adequate for accredited institutions and their regulatory roles and contained in the software_statement. The list of regulatory permissions and the corresponding scopes are described in the following sections;

10. where possible, shall compare client metadata asserted by a client to the metadata provided in the software_statement, choosing values in the SSA with precedence;

11. shall accept all x.500 AttributeType name strings defined in the Distinguished Name of the x.509 Certificate Profiles defined in Open Finance Brasil x.509 Certificate Standards;

12. The value of the field UID of the certificate should match the one sent in the SSA, where the UID field should contain the value of the software_id field of the SSA.

13. shall, during the TLS handshake process, use the distinguishedNameMatch rule to compare the DN values as defined in RFC4517.

14. shall ensure the integrity of the stock of active consents, even after any systemic changes, so that such changes are transparent to the data receiver institutions (TPP).

15. shall perform a recertification on OIDF FAPI and DCR after any systemic changes.

16. The value of the software_api_webhook_uris attribute contained as an attribute in the JWS in software_statement must be compared with the webhook_uris field. If the values are not exactly the same, the error must be returned, with the HTTP status code set to 400, error filled in as invalid_webhook_uris and error_description filled in with The content of the webhook_uris field different from what was Registered in the software_statement noted via the JWS software_api_webhook_uris field.

17. If the webhook_uris field is not declared in the payload, the webhook functionality shall be considered disabled for the specific client.

These provisions apply equally to the processing of RFC7591, RFC7592 and OpenID Registration requests

7.1.1. Applying Server Defaults

Whenever properties of a DCR request are not included nor mandatory in the specification, the Authorisation Server shall apply client defaults in the following manner:

1. shall select and apply the encryption algorithm and cipher choice from the most recommended of the IANA cipher suites that is supported by the Authorisation Server;

2. shall populate defaults from values within the software_statement assertion where possible;

3. shall grant the client permission to the complete set of potential scopes based on the softwares regulatory permissions included in the software_statement;

7.2. Regulatory Roles for OpenID and OAuth 2.0 Mappings

To participate in the Open Finance ecosystem, accredited institutions must register themselves in the directory of participants according to their regulatory roles. Those roles reflect the institutions authorization from the Central Bank and, consequently, the APIs they are allowed to use.

The following table describes the regulatory roles for Open Finance and the related OAuth 2.0 scopes mapping. If the scopes are omitted during the DCR process, the authorization server shall grant the complete set of potential scopes based on the registering bank's regulatory roles, as described in the Server Defaults section.

It is requiread that the active roles in the application's software_statement are validated. The field _software_statement_roles shall be used for validation and currently listed roles shall be active.

8. Software Statement Assertion

A Software Statement Assertion (software_statement) is a JSON Web Token (JWT) RFC7519 that asserts the metadata values of the client software as a whole. On the Open Finance Brasil structure, this software_statement is signed by the Participants Directory and it's signature MUST be validated by the Authorization Servers using the public keys available on the following session.

8.1. Attributes of the Software Statement Assertion (Claims)

The following example contains all attributes currently included in a software_statement:

9. Processing of the Dynamic Client Registration claim

Open

9.1. Sending a Registration Claim with a Software Statement

This example includes several optional fields, some of those may not be applicable to some implememntations. For a complete guide to attributes and its mandate, consult the DCR Swagger OFB-DCR/DCM-Swagger. Line breaks inside values serve presentation purposes only.

9.2. Open Finance Brasil SSA Key Store and Issuer Details

The following links point to public keys of the Participant Directory and must be used to verify the signature validity of the software_statements presented during the client registration process.

Production

https://keystore.directory.openbankingbrasil.org.br/openbanking.jwks

Open Finance Open Finance Brasil production SSA issuer

Sandbox

https://keystore.sandbox.directory.openbankingbrasil.org.br/openbanking.jwks

Open Finance Open Finance Brasil sandbox SSA issuer

9.3. About authentication and authorization mechanisms for DCR and DCM services

As they are auxiliary services to the main flow of Open Finance Brasil, the dynamic registration and maintenance services for clients do not use the same access control mechanisms. For example, it is not possible to require an OAuth 2.0 access_token from a client application that isn't registered yet with the transmitting institution.

To extend RFC7591 and RFC7592, which recommend minimum mechanisms for authentication of their services, institutions that support the registration flows and dynamic maintenance of clients must implement the following controls:

9.3.1. Client registration - POST /register

1. validate that the certificate presented by the client application is subordinate to the ICP-Brasil chains defined in the Open Finance Brasil Certificates Standard;

2. ensure that the signature of the software_statement_ presented by the client application during registration has been made by the Directory of Participants using the public keys described in the previous section;

3. ensure that the software_statement presented by the client application during registration corresponds to the same institution as the client certificate presented, validating it through the attributes that bring organization_id in the X.509 certificate.

4. Multiple DCR registrations for the same Software Statement should not be allowed, in a way that in case of a new registration attempt for an already registered Software Statement, the Error Response procedure defined on item 3.2.2 of the RFC7591 must be enforced.

5. issue, on the registry response, a registration_access_token to be used as an authentication token on maintaining operations of the registered client application, following specifications described in RFC7592.

9.3.2. Client Maintenance - GET /register - PUT /register - DELETE /register

1. Validate the presence and matching of the Bearer header Authorization containing the value of the registration_access_token attribute returned during registration of the corresponding client.

2. When the invoked method is PUT / register, carry out the validations of sub-items 1, 2, 3, and 5 of item Client registration - POST /register.

3. When the invoked method is GET /register, carry out the validations of sub-items 1 and 5 of item Client registration - POST /register.

4. When the invoked method is DELETE /register, carry out the validation of sub-item 1 of item Client registration - POST /register.

9.4. Signature certificates validation

• The directory uses cert rescan function hourly to validation process. 

• The organization shall ensure that the validation process was completed.

• Each organization must have a continuity plan in case of unavailability validation service.

• If the signature certificate is not valid because it has a revoked status according to the CA’s OCSP/CRL issuer, or is inactive in the directory register, the set of public keys is moved to the inactive key storage.

• The validation process should include:

  • Resource server (Data Transmitter) message signature validation, to be done by the Client (Data Receiver)

    • Validate that the message was signed in line with what’s defined on the Message Signature Guidelines, including that the iss is equal to the organisation_id of the server that issued the message.

    • Fetch the “iss” claim from the JWT and build the directory application JWKS uri for that specific server.

    • Make sure that the kid present on the message JWT header is present on the directory JWKS.

    • Validate that the private key for the corresponding kid is able to validate the message signature.

  • Client (Data Receiver) message signature validation, to be done by the Resource Server

    • Validate how the message was signed in line with what’s defined on the Message Signature Guidelines.

    • Obtain the org_jwks_uri which was presented on the SSA by the client on the moment of the registration (DCR)

    • Make sure that the kid present on the message JWT header is present on the directory JWKS.

    • Validate that the private key for the corresponding kid is able to validate the message signature.

10. Acknowledgement

With thanks to all who have set the foundations for secure and safe data sharing through the formation of the OpenID Foundation FAPI Working Group, the Open Finance Brasil GT Security and to the pioneers who will stand on their shoulders.

The following people contributed to this document:

• Alexandre Daniel Dalabrida (Cooperativa Central Ailos)

• Alexandre Siqueira (Mercado Pago)

• André Borges (Banco Fibra)

• Bernardo Vale (Banco Inter)

• Caio Zanolla (Belvo)

• Danilo Sasaki (Banco Itaú)

• João Rodolfo Vieira da Silva (Banco Itaú)

• Michelle Bandarra (Chicago)

• Nic Marcondes (Quanto)

• Rafael Gonzalez Hashimoto (Banco C6)

• Ralph Bragg (Raidiam)

Appendix A. Notices

Copyright (c) 2023 Open Finance Brasil Initial Structure.

The Open Finance Brasil Initial Structure (OFBIS) grants to any Contributor, developer, implementer, or other interested party a non-exclusive, royalty-free, worldwide copyright license to reproduce, prepare derivative works from, distribute, perform and display, this Implementers Draft or Final Specification solely for the purposes of (i) developing specifications, and (ii) implementing Implementers Drafts and Final Specifications based on such documents, provided that attribution be made to the OFBIS as the source of the material, but that such attribution does not indicate an endorsement by the OFBIS.

The technology described in this specification was made available from contributions from various sources, including members of the OpenID Foundation, the Open Finance Brasil GT Security Working Group and others. Although the Open Finance Brasil Initial Structure has taken steps to help ensure that the technology is available for distribution, it takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this specification or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any independent effort to identify any such rights. The Open Finance Brasil Initial Structure and the contributors to this specification make no (and hereby expressly disclaim any) warranties (express, implied, or otherwise), including implied warranties of merchantability, non-infringement, fitness for a particular purpose, or title, related to this specification, and the entire risk as to implementing this specification is assumed by the implementer. The Open Finance Brasil Intellectual Property Rights policy requires contributors to offer a patent promise not to assert certain patent claims against other contributors and against implementers. The Open Finance Brasil Initial Structure invites any interested party to bring to its attention any copyrights, patents, patent applications, or other proprietary rights that may cover technology that may be required to practice this specification.

A.1. Appendix A. Example Software Statement Assertion

Author's Address

OFBIS GT Security

Open Finance Brasil Initial Structure

Email: gt-seguranca@openfinancebrasil.org.br

URI: https://openfinancebrasil.org.br