README.md in sensu-plugins-aws-8.3.1 vs README.md in sensu-plugins-aws-9.0.0

@@ -250,6 +250,29 @@
 ```
 ## Installation
 
 [Installation and Setup](http://sensu-plugins.io/docs/installation_instructions.html)
 
-Note:  In addition to the standard installation requirements the installation of this gem will require compiling the nokogiri gem.  Due to this you'll need certain developmemnt packages on your system.  On Ubuntu systems install build-essential, libxml2-dev and zlib1g-dev.  On CentOS install gcc and zlib-devel.
+Note:  In addition to the standard installation requirements the installation of this gem will require compiling the nokogiri gem.  Due to this you'll need certain development packages on your system.  On Ubuntu systems install build-essential, libxml2-dev and zlib1g-dev.  On CentOS install gcc and zlib-devel.
+
+## Authentication
+
+AWS credentials are required to execute these checks. Starting with AWS-SDK v2 there are a few
+methods of passing credentials to the check:
+
+1. Use a [credential file](http://docs.aws.amazon.com/sdk-for-ruby/v2/developer-guide/setup-config.html#aws-ruby-sdk-credentials-shared). Place the credentials in `~/.aws/credentials`. On Unix-like systems this is going to be `/opt/sensu/.aws/credentials`. Be sure to restrict the file to the `sensu` user.
+```
+[default]
+aws_access_key_id = <access_key>
+aws_secret_access_key = <secret_access_key>
+```
+
+2. Use an [EC2 instance profile](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html). If the checks are executing on an EC2 instance you can give the instance an IAM role and authentication will be handled automatically.
+
+See the [AWS-SDK docs](http://docs.aws.amazon.com/sdkforruby/api/#Configuration) for more details on
+credential configuration.
+
+Some of the checks accept credentials with `aws_access_key` and `aws_secret_access_key` options
+however this method is deprecated as it is insecure to pass credentials on the command line. Support
+for these options will be removed in future releases.
+
+No matter which authentication method is used you should restrict AWS API access to the minimum required to run the checks. In general this is done by limiting the sensu IAM user/role to the necessary `Describe` calls for the services being checked.