# Enable authentication
source: https://developer.mastercard.com/mastercard-checkout-solutions/tutorial/use-postman-for-mastercard-checkout-services-apis/step4/index.md

## 3. Enable authentication {#3-enable-authentication}

Mastercard supports OAuth 1.0a for authenticating client applications in order to call our APIs. The type of authentication may differ from service to service. Read [API basics](https://developer.mastercard.com/mastercard-checkout-solutions/documentation/api-basics/index.md) section for more details.

Depending on the authentication mechanism used by the service you wish to call, choose the relevant set of instructions below.

## OAuth 1.0a {#oauth-10a}

Choose from one of the following ways:

Navigate to your environment and set the values for the following variables in the `Current value` field:

![Postman](https://static.developer.mastercard.com/content/mastercard-checkout-solutions/documentation/images/postman-setup-baseurl.png "Postman")

* `baseUrl`: Get the Sandbox URL value from your API specification.
  ![Postman](https://static.developer.mastercard.com/content/mastercard-checkout-solutions/documentation/images/postman-get-baseurl-from-api.png "Postman")

* `consumerKey`: Enter the Consumer key displayed after successfully creating the API Signing Key on MC Connect Onboarding portal. Read [Key Management](https://developer.mastercard.com/mastercard-checkout-solutions/tutorial/key-management/add-signing-key/index.md) for more details.

* `privateKey`: You must have downloaded .p12 certificate after successfully creating the API Signing Key on MC Connect Onboarding portal, as described in [Key Management](https://developer.mastercard.com/mastercard-checkout-solutions/tutorial/key-management/add-signing-key/index.md) tutorial.   
  Extract the private RSA key from the .p12 certificate using the following command in OpenSSL. When prompted, use the password/passphrase values of your .p12 file that you used while creating the API Signing Key.

* OpenSSL:

```OpenSSL:
  openssl pkcs12 -in 'mykey.p12' | openssl rsa -out myrsa.key
  
```

<br />

Click on your collection, navigate to the **Authorization** tab, configure the values as stated below and save the changes:
![Postman](https://static.developer.mastercard.com/content/mastercard-checkout-solutions/documentation/images/postman-authorization.png "Postman")

|                       Parameter                        |                                                                                                                                                                                                                                                            Value                                                                                                                                                                                                                                                            |
|--------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Auth Type                                              | OAuth 1.0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| Add auth data to                                       | Request Headers                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Signature Method                                       | RSA-SHA256                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Consumer Key                                           | {{consumerKey}} - Enter the consumer key displayed after successfully creating the API Signing Key on MC Connect Onboarding portal. Read [Key Management](https://developer.mastercard.com/mastercard-checkout-solutions/tutorial/key-management/add-signing-key/index.md) for more details.                                                                                                                                                                                                                                |
| Private Key                                            | {{privateKey}} - You must have downloaded .p12 certificate after successfully creating the API Signing Key on MC Connect Onboarding portal, as described in [Key Management](https://developer.mastercard.com/mastercard-checkout-solutions/tutorial/key-management/add-signing-key/index.md) tutorial. Extract the private RSA key from the .p12 certificate using the following command in OpenSSL. When prompted, use the password/passphrase values of your .p12 file that you used while creating the API Signing Key. |
| In Advanced configuration, check **Include body hash** | Select this checkbox.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |

* OpenSSL:

```OpenSSL:
  openssl pkcs12 -in 'mykey.p12' | openssl rsa -out myrsa.key
  
```