docs: Support use of alias field

Author: ps863

docs/configuration.md

@@ -28,6 +28,7 @@ For example, the config object may look similar to the following:
 | eventPluginsToLoad | [Plugin](examples.md#record-custom-events-using-a-plugin)[] | `[]` | The set of custom plugins to load. See [usage examples](examples.md#record-custom-events-using-a-plugin). |
 | guestRoleArn | String | `undefined` | The ARN of the AWS IAM role that will be assumed during anonymous authorization.<br/><br/>When `guestRoleArn` and `identityPoolId` are both set, the web client will use Cognito's [basic (classic) authflow](https://docs.aws.amazon.com/cognito/latest/developerguide/authentication-flow.html).<br/><br/>When only `identityPoolId` is set, the web client will use Cognito's [enhanced (simplified) authflow](https://docs.aws.amazon.com/cognito/latest/developerguide/authentication-flow.html) (recommended). |
 | identityPoolId | String | `undefined` | The Amazon Cognito Identity Pool ID that will be used during anonymous authorization.<br/><br/>When `identityPoolId` is set, the web client will use Cognito to retrieve temporary AWS credentials. These credentials authorize the bearer to send data to the CloudWatch RUM app monitor.<br/><br/>When`identityPoolId` is not set, you must either (A) forward credentials to the web client using the `setAwsCredentials` command, or (B) use a proxy and set `signing` to `false`. |
+| alias | String | `undefined` | Adds an alias to all PutRumEvents requests. This will be compared against the `rum:alias` service context key in the resource based policy attached to a RUM app monitor. To learn more about how to use resource based policies with RUM, see [here](http://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch-RUM-resource-policies.html). |
 | pageIdFormat | String | `'PATH'` | The portion of the `window.location` that will be used as the page ID. Options include `PATH`, `HASH` and `PATH_AND_HASH`.<br/><br/>For example, consider the URL `https://amazonaws.com/home?param=true#content`<br/><br/>`PATH`: `/home`<br/>`HASH`: `#content`<br/>`PATH_AND_HASH`: `/home#content` |
 | pagesToInclude | RegExp[] | `[/.*/]` | A list of regular expressions which specify the `window.location` values for which the web client will record data, unless explicitly excluded by `pagesToExclude`. Pages are matched using the `RegExp.test()` function.<br/><br/>For example, when `pagesToInclude: [ /\/home/ ]`, then data from `https://amazonaws.com/home` will be included, and `https://amazonaws.com/` will not be included. |
 | pagesToExclude | RegExp[] | `[]` | A list of regular expressions which specify the `window.location` values for which the web client will not record data. Pages are matched using the `RegExp.test()` function.<br/><br/>For example, when `pagesToExclude: [ /\/home/ ]`, then data from `https://amazonaws.com/home` will be excluded, and `https://amazonaws.com/` will not be excluded. |