Initial pass adding AWS IAM Authentication #1263

This adds AWS IAM authentication as a replacement for defining a
password in the configuration.

When the configuration option :use_iam_authentication = true, an
authentication token (password) will be fetched from IAM and cached
for the next 14 minutes (tokens expire in 15 minutes).  These can then
be reused by all new connections until it expires, at which point a
new token will be fetched when next needed.

To allow for multiple Mysql2::Client configurations to multiple
servers, the cache is keyed by database username, host name, port, and
region.

Two new configuration options are necessary:
- :use_iam_credentials = true
- :host_region is a string region name, e.g. 'us-east-1'.  If not set,
  ENV['AWS_REGION'] will be used.  If this is not present,
  authenticaiton will fail.

As prerequisites, you must enable IAM authentication on the RDS
instance, create an IAM policy, attach the policy to the target IAM
user or role, create the database user set to use the AWS
Authentication Plugin, and then run your ruby code using that user or
role.  See
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/UsingWithRDS.IAMDBAuth.Connecting.html
for details on these steps.

You must include the aws-sdk-rds gem in your bundle to use this feature.

README.md

@@ -284,8 +284,10 @@ Mysql2::Client.new(
   :get_server_public_key = true/false,
   :default_file = '/path/to/my.cfg',
   :default_group = 'my.cfg section',
-  :default_auth = 'authentication_windows_client'
-  :init_command => sql
+  :default_auth = 'authentication_windows_client',
+  :init_command => sql,
+  :use_iam_authentication => true/false,
+  :host_region,
   )
 ```
 
@@ -348,6 +350,32 @@ When secure_auth is enabled, the server will refuse a connection if the account
 The MySQL 5.6.5 client library may also refuse to attempt a connection if provided an older format password.
 To bypass this restriction in the client, pass the option `:secure_auth => false` to Mysql2::Client.new().
 
+### AWS IAM Authentication
+
+You may use AWS IAM Authentication instead of setting a password in
+the configuration.  A temporary token used in place of the password
+will be fetched as necessary and used for connections until it
+expires.  The value for :host_region will either use the one provided,
+or if not provided, the environment variable AWS_REGION.
+
+You must add the `aws-sdk-rds` gem to your bundle to use this functionality.
+
+| `:use_iam_authentication` | true                                 |
+| ---                       | ---                                  |
+| `:username`               | The database username configured to use IAM Authentication |
+| `:host`                   | The database host |
+| `:port`                   | The database port |
+| `:host_region`            | An AWS region name, e.g. `us-east-1` |
+
+As prerequisites, you must enable IAM authentication on the RDS
+instance, create an IAM policy, attach the policy to the target IAM
+user or role, create the database user set to use the AWS
+Authentication Plugin, and then run your ruby code using that IAM user or
+role.  See
+[AWS documentation](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/UsingWithRDS.IAMDBAuth.Connecting.html)
+for details on these steps.
+
+
 ### Flags option parsing
 
 The `:flags` parameter accepts an integer, a string, or an array. The integer

lib/mysql2.rb

@@ -38,6 +38,7 @@
 require 'mysql2/client'
 require 'mysql2/field'
 require 'mysql2/statement'
+require 'mysql2/aws_iam_auth'
 
 # = Mysql2
 #

lib/mysql2/aws_iam_auth.rb

@@ -0,0 +1,68 @@
+require 'singleton'
+
+module Mysql2
+  # Generates and caches AWS IAM Authentication tokens to use in place of MySQL user passwords
+  class AwsIamAuth
+    include Singleton
+    attr_reader :mutex
+    attr_accessor :passwords
+
+    # Tokens are valid for up to 15 minutes.
+    # We will assume ours expire in 14 minutes to be safe.
+    TOKEN_EXPIRES_IN = (60 * 14) # 14 minutes
+
+    def initialize
+      begin
+        require 'aws-sdk-rds'
+      rescue LoadError
+        puts "gem aws-sdk-rds was not found.  Please add this gem to your bundle to use AWS IAM Authentication."
+        exit
+      end
+
+      @mutex = Mutex.new
+      # Key identifies a unique set of authentication parameters
+      # Value is a Hash
+      # :password is the token value
+      # :expires_at is (just before) the token was generated plus 14 minutes
+      @passwords = {}
+      instance_credentials = Aws::InstanceProfileCredentials.new
+      @generator = Aws::RDS::AuthTokenGenerator.new(:credentials => instance_credentials)
+    end
+
+    def password(user, host, port, opts)
+      params = to_params(user, host, port, opts)
+      key = key_from_params(params)
+      passwd = nil
+      AwsIamAuth.instance.mutex.synchronize do
+        begin
+          passwd = @passwords[key][:password] if @passwords.dig(key, :password) && Time.now.utc < @passwords.dig(key, :expires_at)
+        rescue KeyError
+          passwd = nil
+        end
+      end
+      return passwd unless passwd.nil?
+
+      AwsIamAuth.instance.mutex.synchronize do
+        @passwords[key] = {}
+        @passwords[key][:expires_at] = Time.now.utc + TOKEN_EXPIRES_IN
+        @passwords[key][:password] = password_from_iam(params)
+      end
+    end
+
+    def password_from_iam(params)
+      @generator.auth_token(params)
+    end
+
+    def to_params(user, host, port, opts)
+      params = {}
+      params[:region] = opts[:host_region] || ENV['AWS_REGION']
+      params[:endpoint] = "#{host}:#{port}"
+      params[:user_name] = user
+      params
+    end
+
+    def key_from_params(params)
+      "#{params[:user_name]}/#{params[:endpoint]}/#{params[:region]}"
+    end
+  end
+end

lib/mysql2/client.rb

@@ -94,6 +94,11 @@ def initialize(opts = {})
       socket = socket.to_s unless socket.nil?
       conn_attrs = parse_connect_attrs(opts[:connect_attrs])
 
+      if opts[:use_iam_authentication]
+        aws = Mysql2::AwsIamAuth.instance
+        pass = aws.password(user, host, port, opts)
+      end
+
       connect user, pass, host, port, database, socket, flags, conn_attrs
     end