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Financial API - Part 1: Read Only API Security Profile was prepared by OpenID Foundation Financial API Work Group.
Financial API consists of the following parts, under the general title Financial Services — Financial API:
This part is intended to be used with RFC6749, RFC6750, [RFC6736], and OIDC.
In many cases, Fintech services such as aggregation services uses screen scraping and stores user passwords. This model is both brittle and insecure. To cope with the brittleness, it should utilize an API model with structured data and to cope with insecurity, it should utilize a token model such as OAuth [RFC6749, RFC6750].
This working group aims to rectify the situation by developing a REST/JSON model protected by OAuth. Specifically, the FAPI WG aims to provide JSON data schemas, security and privacy recommendations and protocols to:
Both commercial and investment banking accounts as well as insurance, and credit card accounts are to be considered.
This document specifies the method of
This document is applicable to both commercial and investment banking accounts as well as insurance, and credit card accounts are to be considered.
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.
RFC2616 - Hypertext Transfer Protocol -- HTTP/1.1
RFC4122 A Universally Unique IDentifier (UUID) URN Namespace
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
RFC5246 - The Transport Layer Security (TLS) Protocol Version 1.2
RFC7525 - Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)
RFC6125 - Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)
O2fNA - OAuth 2.0 for Native Apps
RFC6819 - OAuth 2.0 Threat Model and Security Considerations
OIDC - OpenID Connect Core 1.0 incorporating errata set 1
OIDD - OpenID Connect Discovery 1.0 incorporating errata set 1
OIDM - OAuth 2.0 Multiple Response Type Encoding Practices
X.1254 - Entity authentication assurance framework
TLSM - Mutual X.509 Transport Layer Security (TLS) Authentication for OAuth Clients
For the purpose of this standard, the terms defined in RFC6749, RFC6750, RFC7636, OpenID Connect Core apply.
API – Application Programming Interface
CSRF - Cross Site Request Forgery
FAPI - Financial API
FI – Financial Institution
HTTP – Hyper Text Transfer Protocol
REST – Representational State Transfer
TLS – Transport Layer Security
The OIDF Financial API (FAPI) is a REST API that provides JSON data representing accounts and transactions related data. These APIs are protected by the OAuth 2.0 Authorization Framework that consists of RFC6749, RFC6750, RFC7636, and other specifications.
These API accesses have several levels of risks associated to them. Read only access is generally speaking associated with lower financial risk than the write access. As such, the characteristics required to the tokens are also different.
In the following subclauses, the method to obtain tokens are explained separately.
Read Only Access typically is the lower risk scenario compared to the Write access, so the protection level can also be lower. However, since the FAPI would provide potentially sensitive information, it requires more protection level than a basic RFC6749 requires.
As a profile of The OAuth 2.0 Authorization Framework, this document mandates the following to the Read Only API of the FAPI.
The Authorization Server
S256 as the code challenge method;redirect_uri parameter in the authorization request;redirect_uri to exactly match one of the pre-registered Redirect URIs;should provide a mechanism for the end-user to revoke access tokens and refresh tokens granted to a Client as in 16.18 of OIDC.
NOTE: The Financial API server may limit the scopes for the purpose of not implementing certain APIs.
NOTE: Section 4.1.3 of RFC6749 does not say anything about the code reuse, but this document is putting limitation on it as per Section 3.1.3.2 of OIDC.
NOTE: If replay identification of the authorization code is not possible, it is desirable to set the validity period of the authorization code to one minute or a suitable short period of time. The validity period may act as a cache control indicator of when to clear the authorization code cache if one is used.
Further, if it wishes to provide the authenticated user's identifier to the client in the token response, the authorization server
openid was included in the requested scope as in Section 3.1.3.3 of OIDC with its sub value equal to the value of the CustomerId of the Customer object corresponding to the authenticated user and optional acr value in ID Token.A Public Client
S256 as the code challenge method for the RFC7636;Further, if it wishes to obtain a persistent identifier of the authenticated user, it
openid in the scope value; andshall include nonce parameter defined in Section 3.1.2.1 of OIDC in the authentication request.
NOTE: Adherence to RFC7636 means that the token request includes code_verifier parameter in the request.
In addition to the provision to the Public Client, the Confidential Client
The FAPI endpoints are OAuth 2.0 protected resource endpoints that return financial information for the resource owner associated with the submitted access token.
The resource server with the FAPI endpoints
Content-type HTTP header Content-Type: application/json; charset=UTF-8;x-fapi-interaction-id to the value received from the corresponding fapi client request header or to a RFC4122 UUID value if the request header was not provided to track the interaction, e.g., x-fapi-interaction-id: c770aef3-6784-41f7-8e0e-ff5f97bddb3a; andshall log the value of x-fapi-interaction-id in the log entry.
NOTE: While this document does not specify the exact method to find out the user associated with the access token and the granted scope, the protected resource can use OAuth Token Introspection [RFC7662].
Further, it
should support the use of Cross Origin Resource Sharing (CORS) [CORS] and or other methods as appropriate to enable Java Script Clients to access the endpoint if it decides to provide access to Javascript clients.
NOTE: Providing access to Javascript clients or not has different security properites.;
The client supporting this document
User-Agent header that identifies the client, e.g., User-Agent: Intuit/1.2.3 Mint/4.3.1; andshall send x-fapi-financial-id whose value is the unique identifier of the desired financial institution to interact assigned by the service bureau where the API is provided by a service bureau which uses the same endpoint for multiple institutions.
NOTE: Conceptually, the value of the x-fapi-financial-id corresponds to iss in the ID Token but is not required to be an https URI. It often is the routing number of the FI.
NOTE: The use of User-Agent and x-fapi-financial-id is not a security feature.
Further, the client
sub value associated with the customer with the x-fapi-customer-id request header, e.g., x-fapi-customer-id: a237cb74-61c9-4319-9fc5-ff5812778d6b;x-fapi-customer-last-logged-time header where the value is supplied as w3c date , e.g., x-fapi-customer-last-logged-time: Tue, 11 Sep 2012 19:43:31 UTC; andx-fapi-customer-ip-address header, e.g., x-fapi-customer-ip-address: 198.51.100.119; andx-fapi-interaction-id request header whose value is a RFC4122 UUID to the server to help correlate log entries between client and server, e.g., x-fapi-interaction-id: c770aef3-6784-41f7-8e0e-ff5f97bddb3a.Since confidential information is being exchanged, all interactions shall be encrypted with TLS/SSL (HTTPS) in accordance with the recommendations in RFC7525. TLS version 1.2 or later shall be used for all communications.
Authorization request and response are not authenticated. For a higher risk scenarios, it should be taken care of. See Part 2, which uses request object to achieve the message source authentication.
Authorization request is not message integrity protected thus request tampering and parameter injection are possible. Where the protection is desired, it should use Part 2.
The response is integrity protected when ID Token is returned from the authorization endpoint.
In this document, the authorization request is not encrypted. Thus, it is possible to leak the information contained if the browser was infected with virus, etc.
Authorization response can be encrypted as ID Token can be encrypted.
It is possible to leak the information through the logs if the parameters were recorded in the logs and the access to the logs are compromised. Strict access control to the logs in such cases should be enforced.
It is possible to leak the information through the logs if the parameters were recorded in the logs and the access to the logs are compromised. Strict access control to the logs in such cases should be enforced.
Care should be taken so that the sensitive data will not be leaked through the referrer.
If the access token is a bearer token, it is possible to exercise the stolen token. Since the access token can be used against multiple URIs, the risk of it leaking is much larger than the refresh token, which is used only against the token endpoint. Thus, the lifetime of the access token should be much shorter than that of the refresh token. Refer to section 16.18 of OIDC for more discussion on the lifetimes of access tokens and refresh tokens.
Stakeholders should follow the privacy principles of ISO/IEC 29100. In particular:
Following people contributed heavily towards this document.