CloudEvents programming model for Extend by Auth0

This repository provides a webtask middleware that supports a simple programming model for CloudEvents. It can be used by Extend and Auth0 Webtask users to quickly and simply implement CloudEvent consumers and optionally secure it with HTTP basic authentication.

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The JavaScript programming model for CloudEvents implemented in this module requires the user to implement a class with methods representing the supported CloudEvents events. At runtime, messages will be dispatched to specific methods of the class based on the eventType context property of the event. The class can implement any number of methods for different eventType values.

The example below shows how to create a CloudEvent handler on Auth0 Webtasks, but it is just as well applicable to Extend deployments.

First, write the webtask script:

``
cat > cloud-events-handler.js <'use strict';
module.exports = ce => {
ce.on('io.goextend.helloWorld', ctx => {
console.log("Hello, world event received!", ctx.body);
});
// Register for other events here
};
EOF
`

Ensure you have wt-cli installed and configured (this is typically only done once):

`bash
npm install -g wt-cli
npm init
`

Then, create the webtask using:

`bash
wt create cloud-events-handler.js \
--middleware cloudevents-parser \
--middleware cloudevents-extend-api
`

Notice the two middleware parameters. The first one is adding support for parsing application/cloudevents+json requests, which allows accepting CloudEvents messages following the structed content mode of the HTTP binding for CloudEvents. The second middleware adds support for the simple JavaScript programming model above.

You can then take the resulting URL and use it as a consumer of CloudEvents sent over HTTP using the structured content mode. You can test your consumer by making a simple request using curl (substitute your URL in the request below):

`bash
curl -v -X POST https://tjanczuk.sandbox.auth0-extend.com/cloud-events-handler \
-H 'Content-Type: application/cloudevents+json' \
--data-binary '{"eventType":"io.goextend.helloWorld"}'
`

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The cloudevents-extend-api middleware can optionally enforce HTTP Basic authentication. To set it up, specify the username:password pair as the BASIC_AUTH secret when creating your webtask:

`bash
wt create cloud-events-handler.js \
--middleware cloudevents-parser \
--middleware cloudevents-extend-api \
--secret BASIC_AUTH=username:password
`

You must then configure your CloudEvent producer to add HTTP Basic username:password credentials when generating the CloudEvents message. How it is done depends on the specifics of the producer.

The cloudevents-extend-api will reject unauthorized requests with HTTP 403.

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You can provide your CloudEvent handler code with secrets for communicating with external services (e.g. Slack or Twilio):

`bash
wt create cloud-events-handler.js \
--middleware cloudevents-parser \
--middleware cloudevents-extend-api \
--secret TWILIO_KEY=abc \
--secret SLACK_URL=https://...
`

These secrets can be accessed within the code in the following way:

`javascript
'use strict';
module.exports = ce => {
ce.on('io.goextend.helloWorld', ctx => {
let twilio_key = ctx.secrets.TWILIO_KEY;
let slack_url = ctx.secrets.SLACK_URL;
// ...
});
};
`

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You can edit the code of your CloudEvents handler using the Extend Editor by opening up a browser with wt edit cloud-events-handler`:

!image

Extend Editor provides an embedded experience for developing CloudEvent consumers within SaaS platforms that act as CloudEvent producers. Check out Extend by Auth0 for more.