Gift Cards – Security

OAuth2

The Gift Card API 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:

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# "XXX" Should be replaced by value provided by Swebank Pay
# CLIENT_ID/CLIENT_SECRET/VAS_AUTH_SERVER_URL can also be set in docker-compose.yml as environment variables if running with docker
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:

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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

A Hash-based Message Authentication Code (HMAC) is used to verify the data integrity and authenticity of the HTTP requests made towards our API.

An HMAC header therefore needs to be present in every 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:

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HmacSHA512 <user>:<nonce>:<digest>

where digest is a Base64 formatted HMAC SHA512 digest of the following string:

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METHOD\n
RESOURCE\n
USER\
NONCE\n
DATE\n
PAYLOAD\n

Required	Field	Description
	`METHOD`	The requested method (in upper case)
	`RESOURCE`	The path to desired resource (without hostname and any query parameters)
	`NONSE`	A unique value for each request (UUID
	`DATE`	Same as `Transmission-Time` if provided as separate header. Uses ISO8601 standard
	`PAYLOAD`	The body of request

Example request:

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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 text string to digest would then look like the following:

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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 base 64 encode the hashed value. This is the final digest to be provided in the Hmac header.

Final Hmac header value:

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HmacSHA512 user:21a0213e-30eb-85ab-b355-a310d31af30e:oY5Q5Rf1anCz7DRm3GyWR0dvJDnhl/psylfnNCn6FA0NOrQS3L0fvyUsQ1IQ9gQPeLUt9J3IM2zwoSfZpDgRJA==

Postman example script for generation HMAC header

In pre-request script copy/paste the following snippet.

JavaScript

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var user = 'Systemtest';
var secret = 'Systemtest';
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 = request.url.trim().replace(new RegExp('^https?://[^/]+/'), '/'); // strip hostname
    uri_path = uri_path.split("?")[0]; //Remove query parameters
    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

Test client

For more information how to implement the api, see Test Client.