Main.API.Public Payment API.Payment API Client - Payment API Client 
Page of - last modified by Thomas Warren on 2020/01/23 13:42 
Payment API Client 

Thomas Warren

2020/01/23 13:42
Table of Contents
Prerequisites
GitHub
Swagger documentation
Project setup
Security
Security documentation
First App run
Testing application
Build docker image:
Deploy to local docker:

Prerequisites

�	Java 11
�	VueJS
�	Maven
�	Postgres
GitHub

�	Payment Api Client
Swagger documentation

�	Payment API Swagger
Project setup

vas-payment-api-client
├─┬ backend         → backend module with Spring Boot code
│ ├── src
│ └── pom.xml
├─┬ frontend       → frontend module with Vue.js code
│ ├── src
│ └── pom.xml
└── pom.xml         → Maven parent pom managing both modules
Security

Oauth2:
VasPublicPaymentApi requires an OAuth2 access token for interaction.
This application automatically handles token fetching and refreshing by using Spring Security.
Configuration values are set in application.yml:  
# "XXX" Should be replaced by value provided by PayEx
# CLIENT_ID/CLIENT_SECRET/VAS_AUTH_SERVER_URL can also be set in docker-compose.yml as environment variables if running with docker
# The application will see if environment variables are present, if not fall back to "XXX" values.
vas-payment-api:
        oauth2:
                client:
                        grantType: client_credentials
                        clientId: "${CLIENT_ID}:XXX"
                        clientSecret: "${CLIENT_SECRET}:XXX"
                        accessTokenUri: "${VAS_AUTH_SERVER_URL}:XXX"
                        scope: publicapi 
                        
And the implementation of these are located in Oauth2RestTemplateConfiguration.java:
public class Oauth2RestTemplateConfiguration {
      //...
      @Bean
      @ConfigurationProperties("vas-payment-api.oauth2.client")
      protected ClientCredentialsResourceDetails oAuthDetails() {
              return new ClientCredentialsResourceDetails();
      }

      @Bean
      protected RestTemplate restTemplate() {
                var restTemplate = new OAuth2RestTemplate(oAuthDetails());
                restTemplate.setInterceptors(ImmutableList.of(externalRequestInterceptor()));
                restTemplate.setRequestFactory(httpRequestFactory());
              return restTemplate;
      }
      //...
}
HMAC:
The API also requires HMAC authentication to be present in a request.
In this client the HMAC value is automatically calculated by HmacSignatureBuilder.java and added to all outgoing requests in ExternalRequestInterceptor.java
HMAC is implemented using SHA-512 secure hash algorithm.  
Expected Hmac header format is:
HmacSHA512 <user>:<nonce>:<digest>  
where digest is a Base64 formatted HMAC SHA512 digest of the following string:  
METHOD\n
RESOURCE\n
USER\
NONCE\n
DATE\n
PAYLOAD\n
METHOD (mandatory) the requested method (in upper case) RESOURCE (mandatory) the path to desired resource (without hostname and any query parameters)
NONSE (mandatory) a unique value for each request (UUID) DATE(optional) same as Transmission-Time if provided as seperate header. Uses ISO8601 standard PAYLOAD (optional) body of request  
Example request:
curl -X POST \
  https://stage-evc.payex.com/payment-api/api/payments/payment-account/balance \
  -H 'Accept: */*' \
  -H 'Agreement-Merchant-Id: XXX' \
  -H 'Authorization: Bearer XXX' \
  -H 'Hmac: HmacSHA512 user:21a0213e-30eb-85ab-b355-a310d31af30e:oY5Q5Rf1anCz7DRm3GyWR0dvJDnhl/psylfnNCn6FA0NOrQS3L0fvyUsQ1IQ9gQPeLUt9J3IM2zwoSfZpDgRJA==' \
  -H 'Transmission-Time: 2019-06-18T09:19:15.208257Z' \
  -H 'Session-Id: e0447bd2-ab64-b456-b17b-da274bb8428e' \
  -d '{
  "accountIdentifier": {
    "accountKey": "7013369000000000000",
    "cvc": "123",
    "expiryDate": "2019-12-31",
    "instrument": "GC"
  }
}'
In this example USER is user and SECRET is secret.  
The plain string to digest would then be:
POST
/payment-api/api/payments/payment-account/balance
user
21a0213e-30eb-85ab-b355-a310d31af30e
2019-06-18T09:19:15.208257Z
{
  "accountIdentifier": {
    "accountKey": "7013360000000000000",
    "cvc": "123",
    "expiryDate": "2020-12-31",
    "instrument": "CC"
  }
}
The plain digest string is then hashed with HmacSHA512 algorithm and the SECRET. Finally we Base64 encode the hashed value. This is the final digest to be provided in the Hmac header.
Final Hmac header value:  
HmacSHA512 user:21a0213e-30eb-85ab-b355-a310d31af30e:oY5Q5Rf1anCz7DRm3GyWR0dvJDnhl/psylfnNCn6FA0NOrQS3L0fvyUsQ1IQ9gQPeLUt9J3IM2zwoSfZpDgRJA==
Postman example script
In pre-request script copy/paste the following snippet:

var user = 'user';
var secret = 'secret';
var transmissionTime = (new Date()).toISOString();
var sessionId = guid();

var hmac = generateHMAC(user, secret, transmissionTime);
console.log('hmac: ' + hmac);

//Set header values
pm.request.headers.add({key: 'Hmac', value: hmac });
pm.request.headers.add({key: 'Transmission-Time', value: transmissionTime });
pm.request.headers.add({key: 'Session-Id', value: sessionId });

function generateHMAC(user, secret, transmissionTime) {

      var algorithm = "HmacSHA512";
      var separator = ":";
      var method = request.method.toUpperCase();
      var nonce = generateNonce(); //UUID
      var date = transmissionTime;
      
      var uri_path = replaceRequestEnv(request.url.trim()).trim().replace(new RegExp('^https?://[^/]+/'), '/'); // strip hostname
      uri_path = uri_path.split("?")[0]; //Remove query paramters
      var payload = _.isEmpty(request.data) ? "" : request.data;
      var macData = method + '\n'
              + uri_path + '\n'
              + user + '\n'
              + nonce + '\n'
              + date + '\n'
              + payload + '\n';

        macData = replaceRequestEnv(macData);
        console.log('data to mac: ' + macData);

      var hash = CryptoJS.HmacSHA512(macData, secret);
      var digest = CryptoJS.enc.Base64.stringify(hash);
      return algorithm + " " + user + separator + nonce + separator + digest;
}

function replaceRequestEnv(input) { //manually set environments to they are populated before hashing
      return input.replace(/{{([^)]+)}}/g, function (str, key) {
              var value = pm.environment.get(key);
              return value === null ? pm.varables.get(key) : value;
        });
}

function generateNonce() {
      return guid();
}

function guid() {
      function s4() {
              return Math.floor((1 + Math.random()) * 0x10000)
                        .toString(16)
                        .substring(1);
        }

      return s4() + s4() + '-' + s4() + '-' + s4() + '-' +
                s4() + '-' + s4() + s4() + s4();
}
Security documentation

�	OAuth2
�	Client Credentials
�	The RESTful CookBook: HMAC
�	HMAC - Wikipedia
First App run

docker-compose.yml).
Inside the root directory, do a:  
mvn clean install
Run the Spring Boot App:
mvn --projects backend spring-boot:run
Now go to http://localhost:8080/ and have a look at your new client.
Testing application

 1.	Add a new card with provided details from PayEx.
 2.	Click on newly added Card
 3.	Click on "initiate payment" to create a new transaction
Build docker image:

mvn --projects backend clean compile jib:dockerBuild
Deploy to local docker:

docker-compose up -d