# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   autoscaling_launch_config_requires_imdsv2_check
# 
# Description:
#   This control checks whether an Amazon EC2 Auto Scaling launch configuration is configured to require the use of Instance Metadata Service Version 2 (IMDSv2).
# 
# Reports on:
#   AWS::AutoScaling::LaunchConfiguration
# 
# Evaluates:
#   AWS CloudFormation, AWS CloudFormation hook
# 
# Rule Parameters:
#   None
# 
# Scenarios:
#  Scenario: 1
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document does not contain any Autoscaling launch configuration resources
#      Then: SKIP
#  Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Autoscaling launch configuration resource
#       And: 'MetadataOptions' has been provided.
#       And: 'MetadataOptions.HttpEndpoint' has been provided is equal to 'disabled'
#      Then: SKIP
#  Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Autoscaling launch configuration resource
#       And: 'MetadataOptions.HttpEndpoint' has not been provided or has been provided and is equal to 'enabled'
#       And: 'MetadataOptions.HttpTokens' has not been provided
#      Then: FAIL
#  Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Autoscaling launch configuration resource
#       And: 'MetadataOptions' has been provided.
#       And: 'MetadataOptions.HttpEndpoint' has not been provided or has been provided and is equal to 'enabled'
#       And: 'MetadataOptions.HttpTokens' has been provided and set to a value other than 'required'
#      Then: FAIL
#  Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an Autoscaling launch configuration resource
#       And: 'MetadataOptions' has been provided.
#       And: 'MetadataOptions.HttpEndpoint' has not been provided or has been provided and is equal to 'enabled'
#       And: 'MetadataOptions.HttpTokens' has been provided and set to 'required'
#      Then: PASS

#
# Constants
#
let AUTOSCALING_LAUNCH_CONFIGURATION_TYPE = "AWS::AutoScaling::LaunchConfiguration"
let INPUT_DOCUMENT = this

#
# Assignments
#
let autoscaling_launch_configurations = Resources.*[ Type == %AUTOSCALING_LAUNCH_CONFIGURATION_TYPE ]

#
# Primary Rules
#
rule autoscaling_launch_config_requires_imdsv2_check when is_cfn_template(%INPUT_DOCUMENT)
                                                          %autoscaling_launch_configurations not empty {
    check(%autoscaling_launch_configurations.Properties)
        <<
        [CT.AUTOSCALING.PR.2]: Require an Amazon EC2 Auto Scaling group launch configuration to configure Amazon EC2 instances for IMDSv2
        [FIX]: Provide a 'MetadataOptions' configuration and set the value of 'HttpTokens' to 'required'.
        >>
}

rule autoscaling_launch_config_requires_imdsv2_check when is_cfn_hook(%INPUT_DOCUMENT, %AUTOSCALING_LAUNCH_CONFIGURATION_TYPE) {
    check(%INPUT_DOCUMENT.%AUTOSCALING_LAUNCH_CONFIGURATION_TYPE.resourceProperties)
        <<
        [CT.AUTOSCALING.PR.2]: Require an Amazon EC2 Auto Scaling group launch configuration to configure Amazon EC2 instances for IMDSv2
        [FIX]: Provide a 'MetadataOptions' configuration and set the value of 'HttpTokens' to 'required'.
        >>
}

#
# Parameterized Rules
#
rule check(autoscaling_launch_configuration) {
    %autoscaling_launch_configuration [
        # Scenario 2
        filter_autoscaling_launch_configurations(this)
    ] {
        # Scenario 3, 4 and 5
        MetadataOptions exists
        MetadataOptions is_struct

        MetadataOptions {
            HttpTokens exists
            HttpTokens == "required"
        }
    }
}

rule filter_autoscaling_launch_configurations(autoscaling_launch_configurations) {
    %autoscaling_launch_configurations {
        MetadataOptions not exists or
        filter_metadata_options(this)
    }
}

rule filter_metadata_options(metadata_options) {
    %metadata_options {
        MetadataOptions is_struct
        MetadataOptions {
            HttpEndpoint not exists or
            HttpEndpoint == "enabled"
        }
    }
}

#
# Utility Rules
#
rule is_cfn_template(doc) {
    %doc {
        AWSTemplateFormatVersion exists  or
        Resources exists
    }
}

rule is_cfn_hook(doc, RESOURCE_TYPE) {
    %doc.%RESOURCE_TYPE.resourceProperties exists
}