# Paytool External API

#### External API

This chapter provides technical information about the methods created for External application.

<p class="callout info">**Info:** The authentication in our system is handled through the mTLS. To get a certificate please [visit this link.](https://developer.verestro.com/books/connecting-to-our-services-and-sandbox/page/connecting-to-server-to-server-apis-fe-sandbox#bkmrk-for-beta%2Fproduction-0)</p>

##### How to get certificate x509

Generate a key pair:

```
openssl genrsa -out client.key 2048
```

Create a Certificate Signing Request (CSR):

```
openssl req -new -newkey rsa:4096 -keyout companyName.key -out companyName.csr -nodes -subj '/C=US/ST=Florida/L=Miami/O=SomeCompany/OU=main/CN=V-customer-App/emailAddress=example@user.com'
```

Send the `.csr` file to our Chief of the security department: *sebastian.misiewicz@verestro.com*

@swagger="[https://paytool-api.verestro.com/doc/external.yaml"](https://iban-management.upaid.pl/doc/server.yaml)