Workflow for PSD2 Confirmation of Funds API

In this document, we will guide you through each step you need to take in order to access our PSD2 Confirmation of Funds API.

All API calls here are made using mutually authenticated TLS.

References

Open Banking Security Profile

FAPI - FAPI Read-Only profile

FAPI-RW

OIDC Connect Core

MTLS

Terminology & abbreviations

• TPP: the Third-Party Provider accessing the API.
• Client App (or "Client"): an application developed by the TPP for accessing the API.

Prerequisites

Before you can start using our PSD2 APIs, ensure that you fulfill the requirements outlined in this section.

Sandbox

• A registered app on OP Developer: API key and client secret
• Certificates and related keypairs from our certificate generation API for mutually authenticated TLS
• Successful registration via the TPP registration endpoint (incl. functional JWKS endpoints, redirect uris...)

In Test, the host addresses are the following:

Service	Host
Authentication and authorization	https://authorize.psd2-sandbox.op.fi
Business APIs & token endpoints	https://mtls-apis.psd2-sandbox.op.fi
JWKS endpoint for ID token signature verification	https://authorize.psd2-sandbox.op.fi/oauth/jwks/PSD2_OIDC (subject to change)

Production

• Valid AISP/PISP registration and approval from a European financial authority, passported if necessary
• Valid eIDAS certificates: QWAC for establishing MTLS, QSEAL for signing JWTs
• Successful registration via the TPP registration endpoint (incl. functional JWKS endpoints, redirect uris...)

Overview

The PSD2 Confirmation of Funds API is accessed in the following manner:

1. A Request is made for confirming available funds on a card
2. Client App authenticates with Client Credentials flow
3. Client App registers intent at /authorizations
4. End user authentication and authorization
5. Client App receives an Authorization Code and exchanges it for an Access Token
6. Client App creates a funds-confirmation resource and finds the answer in the response body.

Now let's look at each of these steps one by one.

1. End user or a representative service requests confirmation of funds

The end user and/or the service they are consuming requests to know whether the card has a specified amount of money available.

2. TPP app authenticates using the Client Credentials flow and receives an access token with the scope fundsconfirmations.

To begin interacting with the Confirmation of Funds API, the client application authenticates with the Oauth Client Credentials Flow using scope fundsconfirmations. Note that any given request may only contain one scope.

The authorization request has the following format:

POST /oauth/token HTTPS/1.1
Host: mtls-apis.psd2-sandbox.op.fi
Content-Type: application/x-www-form-urlencoded

grant_type=client_credentials&scope=fundsconfirmations&client_id=<APP_CLIENT_ID>&client_secret=<APP_CLIENT_SECRET>

The following cURL call can be used for completing this step. The call assumes that your current directory contains your client certificate (client.crt) and the related private key (key.pem) - both are created by the Registration Helper App.

curl -vk --key key.pem --cert client.crt https://mtls-apis.psd2-sandbox.op.fi/oauth/token -d 'grant_type=client_credentials&scope=fundsconfirmations&client_id=<client_id>&client_secret=<client_secret>'

If the request is successful, the response will look like this:

{
  "token_type" : "bearer",
  "access_token" : "Axqx362CnSmLABgzqcBasG0pxBj9",
  "scope" : "fundsconfirmations",
  "status" : "approved",
  "expires_in" : "86399",
}

Save the access_token for use in the next step.

3. TPP registers intent to confirm funds

Now the TPP application is in possession of an access token. To advance, the TPP establishes mutually authenticated TLS with the host and uses the access token to make a POST call to the /authorizations endpoint. This registers the TPP's intent to access protected data.

Examine and revoke authorizations

The authorizationId can be used for examining the details of the authorization or delete it. Deleting the authorization revokes the entire authorization and cannot be reversed.

4. Authentication and authorization

Authentication and authorization take place between the end user and the auth server of the account servicer. The role of the TPP is to prepare an appropriate JWT request, fill in the necessary query parameters, and perform the redirection.

4.1 Constructing the authorization request

The request is a JSON Web token that has been signed with a QSEALC private key (or a key which emulates QSEALC) using RS256 or ES256. The corresponding public key must be made available at a registered JWKS endpoint (not required in sandbox).

The header and payload of the JWT request have the following structure:

{
  "alg": "ES256",
  "typ": "JWT",
  "kid": "Vi3hb" --> This value varies per key
}
.
{
  "aud": "https://mtls.apis.op.fi",
  "iss": "cu096Eiii4i2c5CeThpf",
  "response_type": "code id_token",
  "client_id": "cu096Eiii4i2c5CeThpf",
  "redirect_uri": "https://tpp-demo-app.test.psd2-aty.aws.op-palvelut.net/oauth/access_token",
  "scope": "openid fundsconfirmations",
  "state": "bb16b497-097f-4528-9380-4305eb760232",
  "nonce": "76fb7d3a-3a14-4bf7-96fd-e770c3c1e33e",
  "max_age": 86400,
  "exp": 1548751018,
  "iat": 1548750118,
  "claims": {
    "userinfo": {
      "authorizationId": {
        "value": "976da7b0-1db2-410d-a5c9-e3a37bc4d7a1",
        "essential": true
      }
    },
    "id_token": {
      "authorizationId": {
        "value": "976da7b0-1db2-410d-a5c9-e3a37bc4d7a1",
        "essential": true
      },
      "acr": {
        "essential": true,
        "values": [
          "urn:openbanking:psd2:sca"
        ]
      }
    }
  }
}
.
<signature>

Field	Type	Required	Legend
typ	string	true	Type of the token. Always gets value JWT .
alg	string	true	The signing algorithm used. Possible values are RS256 and ES256 .
kid	string	true	ID of the signing key. A key corresponding to this value must be available at a public JWKS endpoint. If you have used the registration app in sandbox, this value is found in the field ssaSigningKid in registration-result.txt (the key is in ssa-signing-key-pem).
aud	string	true	Intended audience of the JWT, i.e. the host URL of the API.
iss	string	true	Issuer of the token, i.e. Client ID of the TPP.
response_type	string	true	Specifies the type of the authorization flow. Allowed values are code and code id_token .
client_id	string	true	Unique identifier of the client application.
redirect_uri	string	true	The address to which the end user wil be redirected after authentication and authorization. The access token or error descriptors will be attached to this uri as query parameters.
scope	string	true	Scope names that identify the extent of the requested authorization, as a list of space-separated names. Per the OIDC specification all requests must contain the scope openid . Only one of the following scopes is allowed for each request: accounts, payments, fundsconfirmations. For CoF, the default required value is "openid fundsconfirmations".
state	string	true	A string that will be returned to the TPP. Used for validating responses and correlating requests with responses. Must only contain supported characters specified in RFC 4648 Section 5 , Table 2.
nonce	string	true	A unique string that is used for protecting against replay attacks. Generated by the Client App.
max_age	number	true	Maximum allowed age for the authentication, in seconds.
exp	number	true	Time of expiry of the JWT request (Unix epoch, in seconds).
iat	number	true	Time of issuance of the JWT request (Unix epoch, in seconds).
claims	object	true	Contains information related to the request. The field authorizationId contains the authorizationId obtained while registering intent.
userinfo	object	true	Contains information related to the request. The field authorizationId contains the authorizationId obtained while registering intent.
id_token	object	true	The contents of this field are similar to userinfo.
acr	obj	true	Specifies the requested authorization contexts. Currently, the only allowed value is urn:openbanking:psd2:sca .

Once the body and header have been constructed, follow these steps: 1. Base64Urlencode the header and body separately. Append the body to the header, separating the two parts with a dot. 2. Create a signature by taking a copy of the newly created string and encrypting it with your private key (from QSEALC or emulated) using the algorithm specified in the header. This is the signature. 3. Attach the signature to the encoded header and body with a dot. You'll get something like this:

eyJhbGciOiJIUzI1NiJ9.eyJtc2ciOiJIZWxsbyJ9.N6-M8oOwCq9x820PR6HMtWo-_FL5GeWUSqQ66H2F5kA

Example code for signing JWTs

This code assumes that a file named ssa-signing-key.pem exists in the current directory. In sandbox, developers may use the Registration Helper App, which automatically generates this file.

import * as fs from 'fs';
import * as jwt from 'jsonwebtoken'; 

//claims is a valid pre-created JWT body
const asymmetricSign = (claims: object) => {
  const algorithm = 'ES256';
  const signCert = fs.readFileSync(`./ssa-signing-key.pem`, 'ascii');
  const jwtOptions = {
    header: {
      typ: 'JWT',
      kid: 'BSyrDg'
    },
    algorithm
  };
  return jwt.sign(JSON.stringify(claims), signCert, jwtOptions);
};

Learn more about JWTs on jwt.io. Note that the JWT editor is currently incapable of processing this type of key.

4.2 Redirection

Once the request is complete, the TPP will redirect the customer to OP's auth server. The client app must append the following query parameters to the redirection URI:

• request (the JWT request)
• response_type
• client_id
• scope

The values of the parameters MUST match with those in the JWT request. Remember that all query parameters must be URLencoded.

The redirect will have the following structure:

https://authorize.psd2-sandbox.op.fi/oauth/authorize
?request=<your_JWT_string>
&response_type=code
&client_id=******
&scope=openid%20fundsconfirmations

Direct the customer to this URI in the browser.

4.3 The customer authenticates and authorizes

Authentication and authorization are the business of the customer and the auth server. The customer logs in, selects the authorizations they wish to consent to, and approves or rejects them.

4.4 Access Code and ID Token

Once the auth flow is complete, the auth server performs a redirect to the URI indicated in the JWT request (provided it matches a URI registered to that application). The access token and all other related information will be appended as query parameters.

Success:
<REDIRECT_URI>?state=<state>&code=<authorization_code>

Success with ID token:
<REDIRECT_URI>#state=<state>&code=<authorization_code>&id_token=<id_token>

Error:
<REDIRECT_URI>?state=<state>&error=<error_description>

For example:
https://localhost:8181/oauth/access_token?error=temporarily_unavailable&state=373b23cd-a1b3-449a-810f-cd4b36f7a60c

ID token and recommended validations

ID tokens are created and returned on two occasions:

1. When using response type code id_token in the authorization request. The id token will be delivered in a query parameter attached to the client app's redirect URI. Note that when an ID token is present, the query string is in fact an URI fragment (begins with "#" instead of "?").
2. When requesting a token from a token endpoint and scope includes openid (in OP PSD2, always). The token will be returned in the response body to the token request.

The ID token contains information about the authorization, and provides an additional layer of security.

The ID token contains the following information:

{
  "typ": "JWT",
  "alg": "RS256",
  "kid": "12345"
}
.
{
  "iss": "https://authorize.psd2-sandbox.op.fi",
  "iat": 1234569795,
  "sub": "28c52f98-7541-42a2-9ca0-b86ceac47692",
  "acr": "urn:openbanking:psd2:sca",
  "authorizationId": "28c52f98-7541-42a2-9ca0-b86ceac47692,
  "aud": "s6BhdRkqt3",
  "nonce": "n-0S6_WzA2Mj",
  "exp": 1311281970,
  --ALTERNATIVE 1: AUTHORIZATION CODE FLOW---
  "s_hash": "76sa5dd",
  "c_hash": "asd097d"
  --ALTERNATIVE 2: TOKEN ENDPOINT---
  "rt_hash": "wFsWWP49hHo4sXwwVSHX-A",
  "at_hash": "bSUTLJiqrooANhJJ2X7pPw"
  }
.
{
<<signature>>
}

Field	Type	Legend
iss	string/URI	Issuer of the token.
iat	timestamp	Token issuance time as seconds since 1970-01-01T0:0:0Z.
sub	string	The authorizationId to which the ID token relates to.
acr	string	Authentication Context Class Reference, i.e. field that describes the level of authentication achieved. Currently, only urn:openbanking:psd2:sca is supported.
authorizationId	string	The authorizationId to which the ID token relates to.
aud	string/client ID	Intended audience of the ID token. WIll contain the Client Id of the Client Application.
nonce	string	A value originally provided by the TPP in the request, used for protecting against replay attacks.
exp	timestamp	Time of expiry, i.e. the time after which the token is no longer valid.
s_hash	string, case-sensitive	Returned with authorization code. State hash value: base64Url encoding of the left-most half of the hash of the octets of the ASCII representation of the state value, where the hash algorithm used is the hash algorithm used in the algHeader Parameter of the ID Token's JOSE Header. For instance, if the alg is RS256, hash the code value with SHA-256, then take the left-most 256 bits and base64url encode them. The s_hashvalue is a case sensitive string.
c_hash	string, case-sensitive	Returned with authorization code. Code hash value: base64url encoding of the left-most half of the hash of the octets of the ASCII representation of the code value, where the hash algorithm used is the hash algorithm used in the alg Header Parameter of the ID Token's JOSE Header.
rt_hash	string	Returned from token endpoint. Refresh token hash value: base64url encoding of the left-most half of the hash of the octets of the ASCII representation of the refresh_token value, where the hash algorithm used is the hash algorithm used in the alg Header Parameter of the ID Token's JOSE Header. For instance, if the alg is RS256, hash the refresh_token value with SHA-256, then take the left-most 128 bits and base64url encode them. The rt_hash value is a case sensitive string.
at_hash	string	Returned from token endpoint. Authorization token hash value: base64url encoding of the left-most half of the hash of the octets of the ASCII representation of the access_token value, where the hash algorithm used is the hash algorithm used in the alg Header Parameter of the ID Token's JOSE Header. For instance, if the alg is RS256, hash the access_token value with SHA-256, then take the left-most 128 bits and base64url encode them. The at_hash value is a case sensitive string.

The ID token must be validated following the OIDC spec. In addition, the TPP should do the following:

Alternative 1: ID token received in redirection URI

• Validate the authorizationId against that received earlier
• Validate the signature of the ID token
• Validate s_hash (state hash)
• Validate c_hash (code hash).

Alternative 2: ID token in access token response body

• Validate the authorizationId against that received earlier
• Validate the signature of the ID token
• Validate rt_hash (refresh token hash)
• Validate at_hash (access token hash).

The public key for validating ID token signatures is available at https://authorize.psd2-sandbox.op.fi/oauth/jwks/PSD2_OIDC.

5. Token exchange

At this point the TPP is in possession of an authorization code. Thus must now be exchanged for an access token with a POST call of the following type:

POST /oauth/token HTTPS/1.1
Host: mtls-apis.psd2-sandbox.op.fi
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&code=<code>&redirect_uri=<redirect_uri>&client_id=<APP_CLIENT_ID>&client_secret=<APP_CLIENT_SECRET>

A successful request will yield a response with the following content:

{
  "access_token":"TfOJ0yOywdg8cwthvKUE",
  "refresh_token":"TYiOBpLHMWSgXsTg0SJ7TlqVMhSsWnJ6vxL6dUk9",
  "id_token": "eyJraWQiOiI2ZzNRRU9SY0hNOVdVZTZlcVowZi1wdjNEUEV1Y2NHVTRUdDFVMHo0cFIwIiwiYWxnIjoiUlMyNTYifQ.eyJydF9oYXNoIjoiMDJaODNSbVFqbTYtQWJEYXRkLTBIdyIsIm5vbmNlIjoiMTIzNCIsImF1dGhvcml6YXRpb25JZCI6ImMxMzgxMDM1LTU2OGMtNGUzYS04OGM5LTQ1Mzk2ZTU2OTBlMiIsImlhdCI6MTU1MjQ3NDkyNSwiaXNzIjoiaHR0cHM6Ly9hdXRob3JpemUua2VoaS5vcC1wYWx2ZWx1dC5uZXQiLCJhdF9oYXNoIjoidmU0MnhDS2ExOTJ4MnplV00zaE5wdyIsInN1YiI6InVpZDUwMDczNTA5IiwiZXhwIjoxNTUyNDc4MjI1LCJhY3IiOiJ1cm46b3BlbmJhbmtpbmc6cHNkMjpzY2EiLCJhdWQiOiJPUF90ZXN0X2NsaWVudCJ9.OMxF_fyVTS0af_so533ODdbbVfw3DOHZmzR-Yosl1N8df6zNZ6FIvFt8PjhcNBG2cMUyAIvfwpt9hKcMt0zwtccyVJzUPPL-ArVuiMIysjJiWo5pp_0AyRaeB-ThqlzMG0yBMibILUobOaZJqNZb1fodE6u_eHEjD2kUEHuxCglIGs8Zu47rhXnSY044YUsukhY1XgThmDPXd0T4vZsmfh_1dDGgp5TX6disKXh1ltspukqnimtI8uf9RrihE5QHu83slodFepHXzYBdlr63wOB15QLvVJXJtZgoM9QUmsAlh9efCEvgGGMcVtB04UEfkGWRQye9sQXEGMHW_S7bsA",
  "scope":"openid fundsconfirmations",
  "token_type":"bearer",
  "expires_in":3599,
}

Field	type	Legend
access_token	string	This is the access token. Use as a bearer token in the Authorization header to access protected resources.
refresh_token	string	Can be used to request additional access tokens.
id_token	string	A signed JWT containing information about the authorization. See ID tokens for a full description on the contents and recommended validation procedures for ID tokens.
scope	string	A space-separated list of scope names describing the services to which the token grants authorization.
token_type	string	Token type. Always has the value "bearer".
expires_in	number	The period for which the token is valid, in seconds.

Refreshing

The Client App may request additional access tokens with the refresh token. The request has the following structure:

POST /oauth/token HTTPS/1.1
Host: mtls-apis.psd2-sandbox.op.fi
Content-Type: application/x-www-form-urlencoded

grant_type=refresh_token&refresh_token=<refresh_token>&client_id=<APP_CLIENT_ID>&client_secret=<APP_CLIENT_SECRET>

The response to this request is similar to that of a normal token request.

6. TPP checks the availability of funds

TPP makes a POST call to /funds-confirmations, with the value in the request body. The response body will contain the field fundsAvailable with a simple true/false response to the confirmation request.