REST API direct integration

If you're new to Composer or REST APIs, check out Primer: Integrations and REST
You can also view the videos in Core Lessons 3 - Data and Integrations​
Please note that REST API direction integration makes client side requests when configuring authorization credentials such as authentication headers or API keys. Learn more in Primer: Security

The client side requests may also run into CORS issues in some cases, you can find a good explanation in for example https://blog.container-solutions.com/a-guide-to-solving-those-mystifying-cors-issues​
A REST API direct integration type data resource essentially tells Composer how a specific, JSON-format HTTP REST API can be accessed. It defines things like a base URL, headers, query parameters, available methods, schemas and so on.
You can create new external data resources and edit existing ones via the Data button in the top toolbar.
Prepackaged external data resource configurations are called connectors, and can be installed into your app via the Marketplace.
The resource configuration is split into base configuration and method configurations for GET collection, GET record, POST, PUT/PATCH and DELETE.
Base configuration
Here, you define the main configuration
Resource ID
This is the unique ID for the resource in your app. Good convention is to have the ID be camel case with an initial capital letter, e.g. SalesforceLeads.
Base URL
This is the base URL shared between all methods. For example, if the path to getting a single Salesforce lead would be https://api.salesforce.com/v2/leads/1234, where 1234 is the lead ID, your base URL would be https://api.salesforce.com/v2/leads/.
Base URL should always be configured with a trailing slash.
Path variables
Path variables are used to make parts of the URL dynamic. A path variable must always be linked to the base URL by including it inside curly braces at the appropriate place in the URL.
For example, to make the v2 part of the Salesforce API URL above dynamic, you would change the base URL to https://api.salesforce.com/{apiVersion}/leads and then add a path variable apiVersion .
Path variables are always dynamic – if you wanted to set a static path variable, you should just write the value in the URL itself.
Headers
HTTP headers to be included in every API call made to this external resource.
Query parameters
Query parameters to be included in every API call made to this external resource.
Method configuration
You can configure each method for your RESTful resource separately. Switch between methods via the left panel.
Enabling a method
Initially, all methods are disabled. To enable a method, toggle the switch near the upper-right corner of the screen.
Relative path
This is the relative part of the URL for the current method that will be appended to the base URL when the method is called.
For example, for a traditional RESTful resource, the relative path for a GET record method would be just the record ID as a path variable, i.e. {id}.
Response key
The JSON response from an API might include the actual data we are interested in inside a sub-key of the main response object. Response key defines this sub-key as a dot-separated path.
For example, if our JSON response for a Salesforce lead was something like:
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{
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  "data": {
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    "lead": {
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      // actual lead data here
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    }
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  }
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}    
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We would then define our response key to be data.lead.
Path variables
Path variables work just like in the base configuration, they just target the Relative path instead of the Base URL.
For example, the GET record method would likely have a id path variable.
Headers
Extra HTTP headers to be included whenever the current method is called.
Query parameters
Extra query parameters to be included whenever the current method is called.
For example, a search or limit query parameter would only make sense when configured exclusively for the GET collection method
Testing methods
Methods can be tested via the Test tab.
After getting a successful response, you can auto-detect and set the method schema from the response with the Set schema from response button.
Method schemas
The Schema tab lets you configure schemas for the specific method.
Publishing a data resource configuration to the Marketplace
You can publish a data resource configuration in the Marketplace, which enables you to install it into other apps.

In the data configurator, click the three-dot icon on the far right side of the data resource list item and select Publish in Marketplace.
To install the data resource in another app, simply search for it via the Marketplace, making sure to select the Data tab first.