companion: allow providing any S3 option, closes #1388

Now you can configure any S3 option listed in
https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/S3.html#constructor-property.

It adds a warning about the official S3 names `accessKeyId` and
`secretAccessKey` because you should use the Companion-style names `key`
and `secret` instead.

packages/@uppy/companion/src/companion.js

@@ -212,25 +212,33 @@ const getOptionsMiddleware = (options) => {
   if (options.providerOptions.s3) {
     const S3 = require('aws-sdk/clients/s3')
     const AWS = require('aws-sdk')
-    const config = options.providerOptions.s3
+    const s3ProviderOptions = options.providerOptions.s3
+    const s3Options = Object.assign({
+      signatureVersion: 'v4'
+    }, s3ProviderOptions)
+    // delete options intended for Companion, not S3:
+    delete s3Options.key
+    delete s3Options.secret
+    delete s3Options.conditions
+    delete s3Options.getKey
+
+    if (s3ProviderOptions.accessKeyId || s3ProviderOptions.secretAccessKey) {
+      throw new Error('Found `providerOptions.s3.accessKeyId` or `providerOptions.s3.secretAccessKey` configuration, but Companion requires `key` and `secret` option names instead. Please use the `key` property instead of `accessKeyId` and the `secret` property instead of `secretAccessKey`.')
+    }
+
     // Use credentials to allow assumed roles to pass STS sessions in.
     // If the user doesn't specify key and secret, the default credentials (process-env)
     // will be used by S3 in calls below.
-    let credentials
-    if (config.key && config.secret) {
-      credentials = new AWS.Credentials(config.key, config.secret, config.sessionToken)
+    if (s3ProviderOptions.key && s3ProviderOptions.secret && !s3Options.credentials) {
+      s3Options.credentials = new AWS.Credentials(
+        s3ProviderOptions.key,
+        s3ProviderOptions.secret,
+        s3ProviderOptions.sessionToken)
     }
-    s3Client = new S3({
-      region: config.region,
-      endpoint: config.endpoint,
-      credentials,
-      signatureVersion: 'v4',
-      useAccelerateEndpoint: config.useAccelerateEndpoint
-    })
+    s3Client = new S3(s3Options)
   }
 
   /**
-   *
    * @param {object} req
    * @param {object} res
    * @param {function} next

website/src/docs/companion.md

@@ -290,10 +290,15 @@ See [env.example.sh](https://github.com/transloadit/uppy/blob/master/env.example
 
 ### S3 options
 
-The S3 uploader has some options in addition to the ones necessary for authentication.
+You can supply any [S3 option supported by the AWS SDK](https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/S3.html#constructor-property) in the `providerOptions.s3` object, _except for_ the below:
+
+- `accessKeyId`. Instead, use the `key` option. This is to make configuration names consistent between different Companion features.
+- `secretAccessKey`. Instead, use the `secret` option. This is to make configuration names consistent between different Companion features.
+
+Additionally, some Companion-specific options can be configured:
+
+#### `providerOptions.s3.getKey(req, filename, metadata)`
 
-#### `s3.getKey(req, filename, metadata)`
-a
 Get the key name for a file. The key is the file path to which the file will be uploaded in your bucket. This option should be a function receiving three arguments:
 - `req`, the HTTP request, for _regular_ S3 uploads using the `@uppy/aws-s3` plugin. This parameter is _not_ available for multipart uploads using the `@uppy/aws-s3-multipart` plugin;
 - `filename`, the original name of the uploaded file;
@@ -304,9 +309,11 @@ This function should return a string `key`. The `req` parameter can be used to u
 ```js
 app.use(authenticationMiddleware)
 app.use(uppy.app({
-  s3: {
-    getKey: (req, filename, metadata) => `${req.user.id}/${filename}`,
-    /* auth options */
+  providerOptions: {
+    s3: {
+      getKey: (req, filename, metadata) => `${req.user.id}/${filename}`,
+      /* auth options */
+    }
   }
 }))
 ```