allow to customize the signed CSR return type (#19213)

for #19027, this modifies the website to accept an `deliveryMethod` parameter to
respond with the signed CSR instead of delivering an email.

The current approach also maintains backwards compatibility:

**Response without `deliveryMethod` (unchanged except for custom headers)**

```
$ curl --insecure -v -H 'content-type: application/json' http://localhost:2024/api/v1/deliver-apple-csr -d '{"unsignedCsrData": "foo"}'
*   Trying [::1]:2024...
* Connected to localhost (::1) port 2024
> POST /api/v1/deliver-apple-csr HTTP/1.1
> Host: localhost:2024
> User-Agent: curl/8.4.0
> Accept: */*
> content-type: application/json
> Content-Length: 26
>
< HTTP/1.1 200 OK
< X-Powered-By: Sails <sailsjs.com>
< Cache-Control: no-cache, no-store
< X-Exit: success
< X-Exit-Description: Delivered email to specified email address with certificate signing request attached.
< Content-Type: text/plain; charset=utf-8
< Content-Length: 2
< ETag: W/"2-nOO9QiTIwXgNtWtBJezz8kv3SLc"
< Set-Cookie: sails.sid=s%3AqOZoNKY2CCZ6PFb9fIKaAjtiTKjB7Gum.9jodWIUG6DCNnXu%2Bn%2BF8cJmI%2Fn19Tk%2FdIkDPBl%2BILbI; Path=/; HttpOnly
< Date: Wed, 22 May 2024 18:23:16 GMT
< Connection: keep-alive
< Keep-Alive: timeout=5
<
* Connection #0 to host localhost left intact
OK
```

**Response with `deliveryMethod=json`**

```
$ curl --insecure -v -H 'content-type: application/json' http://localhost:2024/api/v1/deliver-apple-csr?deliveryMethod=json -d '{"unsignedCsrData": "foo"}'
*   Trying [::1]:2024...
* Connected to localhost (::1) port 2024
> POST /api/v1/deliver-apple-csr?alt=json HTTP/1.1
> Host: localhost:2024
> User-Agent: curl/8.4.0
> Accept: */*
> content-type: application/json
> Content-Length: 26
>
< HTTP/1.1 200 OK
< X-Powered-By: Sails <sailsjs.com>
< Cache-Control: no-cache, no-store
< Content-Type: application/json; charset=utf-8
< X-Exit: success
< X-Exit-Description: Delivered email to specified email address with certificate signing request attached.
< X-Exit-Output-Friendly-Name: RSS feed XML
< Content-Length: 26
< ETag: W/"1a-NnuclRv86ZEKA9WB967iUGlz84s"
< Set-Cookie: sails.sid=s%3AbpaKOTbNe4E911qH4z1-12ABGd_z2d2I.mAimDARoZgnq8zpJHcF95y8qFJXX0iky4Suj0HUKjpI; Path=/; HttpOnly
< Date: Wed, 22 May 2024 18:22:07 GMT
< Connection: keep-alive
< Keep-Alive: timeout=5
<
* Connection #0 to host localhost left intact
{"csr":"UEQ5NGJXdy4uLg=="}
```

# Checklist for submitter

- [x] Manual QA for all new/changed functionality

---------

Co-authored-by: Eric <eashaw@sailsjs.com>

website/api/controllers/deliver-apple-csr.js

@@ -4,9 +4,9 @@ module.exports = {
   friendlyName: 'Deliver Apple CSR',
 
 
-  description: 'Generate and deliver a signed certificate signing request to a requesting user\'s email address.',
+  description: 'Generate and optionally deliver a signed certificate signing request to a requesting user\'s email address.',
 
-  extendedDescription: 'Uses the mdm-gen-cert binary to generate a signed CSR for the user and sends the result to the requesting user\'s email address',
+  extendedDescription: 'Uses the mdm-gen-cert binary to generate a signed CSR for the user and optionally sends the result to the requesting user\'s email address',
 
 
   inputs: {
@@ -14,6 +14,12 @@ module.exports = {
       required: true,
       type: 'string',
       description: 'Base64 encoded CSR submitted from the Fleet server or `fleetctl` on behalf of the user.'
+    },
+    deliveryMethod: {
+      type: 'string',
+      description: 'How the signed CSR will be delivered to the user. ',
+      defaultsTo: 'email',
+      isIn: ['email', 'json']
     }
   },
 
@@ -21,7 +27,9 @@ module.exports = {
   exits: {
 
     success: {
-      description: 'Delivered email to specified email address with certificate signing request attached.'
+      description: 'Signed the provided CSR.',
+      outputType: {csr:'string'},
+      outputFriendlyName: 'Signed CSR',
     },
 
     invalidEmailDomain: {
@@ -35,7 +43,7 @@ module.exports = {
 
   },
 
-  fn: async function({unsignedCsrData}) {
+  fn: async function({unsignedCsrData, deliveryMethod}) {
     let path = require('path');
 
     let signingToolExists = await sails.helpers.fs.exists(path.resolve(sails.config.appPath, '.tools/mdm-gen-cert'));
@@ -113,26 +121,42 @@ module.exports = {
       organization: generateCertificateResult.org,
     });
 
-    // Send an email to the user, with the result from the mdm-gen-cert command attached as a plain text file.
-    await sails.helpers.sendTemplateEmail.with({
-      to: generateCertificateResult.email,
-      subject: 'Your certificate signing request from Fleet',
-      from: sails.config.custom.fromEmailAddress,
-      fromName: sails.config.custom.fromName,
-      template: 'email-signed-csr-for-apns',
-      templateData: {},
-      attachments: [{
-        // When the file is provided as an attachment to the Sails helper, it
-        // gets decoded, since we need for the signed CSR to be delivered in
-        // base64 format, we doubly encode the contents before sending the
-        // email.
-        contentBytes: Buffer.from(generateCertificateResult.request).toString('base64'),
-        name: 'apple-apns-csr.txt',
-        type: 'text/plain',
-      }],
-    }).intercept((err)=>{
-      return new Error(`When trying to send a signed CSR to a user (${generateCertificateResult.email}), an error occured. Full error: ${err}`);
-    });
+    // respBody contains the raw response body content, it defaults to
+    // `undefined` as this was the default behavior of this endpoint before the
+    // 'deliveryMethod' parameter was introduced.
+    var respBody;
+    switch(deliveryMethod) {
+      case 'json':
+        this.res.type('application/json');
+        respBody = JSON.stringify({
+          csr: Buffer.from(generateCertificateResult.request).toString('base64'),
+        });
+        break;
+      case 'email':
+        // Send an email to the user, with the result from the mdm-gen-cert command attached as a plain text file.
+        await sails.helpers.sendTemplateEmail.with({
+          to: generateCertificateResult.email,
+          subject: 'Your certificate signing request from Fleet',
+          from: sails.config.custom.fromEmailAddress,
+          fromName: sails.config.custom.fromName,
+          template: 'email-signed-csr-for-apns',
+          templateData: {},
+          attachments: [{
+            // When the file is provided as an attachment to the Sails helper, it
+            // gets decoded, since we need for the signed CSR to be delivered in
+            // base64 format, we doubly encode the contents before sending the
+            // email.
+            contentBytes: Buffer.from(generateCertificateResult.request).toString('base64'),
+            name: 'apple-apns-csr.txt',
+            type: 'text/plain',
+          }],
+        }).intercept((err)=>{
+          return new Error(`When trying to send a signed CSR to a user (${generateCertificateResult.email}), an error occured. Full error: ${err}`);
+        });
+        break;
+      default:
+        throw 'badRequest';
+    }
 
     // Send a message to Slack.
     await sails.helpers.http.post(sails.config.custom.slackWebhookUrlForMDMSignups, {
@@ -140,7 +164,7 @@ module.exports = {
     });
 
 
-    return;
+    return respBody;
   }
 
 };