# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   ec2_launch_template_imdsv2_check
# 
# Description:
#   This control checks whether your Amazon EC2 launch templates are configured with Instance Metadata Service Version 2 (IMDSv2).
# 
# Reports on:
#   AWS::EC2::LaunchTemplate
# 
# 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 EC2 launch template resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EC2 launch template resource
#       And: 'LaunchTemplateData' has not been provided or 'LaunchTemplateData.MetadataOptions.HttpEndpoint' has
#             been provided and 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 EC2 launch template resource
#       And: 'LaunchTemplateData' has been provided
#       And: 'MetadataOptions.HttpEndpoint' in 'LaunchTemplateData' has not been provided or has been provided and
#            is equal to 'enabled'
#       And: 'MetadataOptions.HttpTokens' in 'LaunchTemplateData' 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 EC2 launch template resource
#       And: 'LaunchTemplateData' has been provided
#       And: 'MetadataOptions.HttpEndpoint' in 'LaunchTemplateData' has not been provided or has been provided and
#            is equal to 'enabled'
#       And: 'MetadataOptions.HttpTokens' in 'LaunchTemplateData' 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 EC2 launch template resource
#       And: 'LaunchTemplateData' has been provided
#       And: 'MetadataOptions.HttpEndpoint' in 'LaunchTemplateData' has not been provided or has been provided and
#            is equal to 'enabled'
#       And: 'MetadataOptions.HttpTokens' in 'LaunchTemplateData' has been provided and set to 'required'
#      Then: PASS

#
# Constants
#
let EC2_LAUNCH_TEMPLATE_TYPE = "AWS::EC2::LaunchTemplate"
let INPUT_DOCUMENT = this

#
# Assignments
#
let ec2_launch_templates = Resources.*[ Type == %EC2_LAUNCH_TEMPLATE_TYPE ]

#
# Primary Rules
#
rule ec2_launch_template_imdsv2_check when is_cfn_template(%INPUT_DOCUMENT)
                                           %ec2_launch_templates not empty {
    check(%ec2_launch_templates.Properties)
        <<
        [CT.EC2.PR.1]: Require an Amazon EC2 launch template to have IMDSv2 configured
        [FIX]: Within the 'LaunchTemplateData' property, provide a 'MetadataOptions' configuration and set the value of 'HttpTokens' to 'required'.
        >>
}

rule ec2_launch_template_imdsv2_check when is_cfn_hook(%INPUT_DOCUMENT, %EC2_LAUNCH_TEMPLATE_TYPE) {
    check(%INPUT_DOCUMENT.%EC2_LAUNCH_TEMPLATE_TYPE.resourceProperties)
        <<
        [CT.EC2.PR.1]: Require an Amazon EC2 launch template to have IMDSv2 configured
        [FIX]: Within the 'LaunchTemplateData' property, provide a 'MetadataOptions' configuration and set the value of 'HttpTokens' to 'required'.
        >>
}

#
# Parameterized Rules
#
rule check(launch_template) {
    %launch_template [
        # Scenario 2
        filter_launch_template_imds_enabled(this)
    ] {
        LaunchTemplateData exists
        LaunchTemplateData is_struct

        LaunchTemplateData {
            # Scenario 3, 4 and 5
            MetadataOptions exists
            MetadataOptions is_struct
            MetadataOptions {
                HttpTokens exists
                HttpTokens == "required"
            }
        }
    }
}

rule filter_launch_template_imds_enabled(launch_template) {
    %launch_template {
        LaunchTemplateData exists
        LaunchTemplateData is_struct
        LaunchTemplateData {
            MetadataOptions not exists or
            filter_metadata_options_imds_enabled(this)
        }
    }
}

rule filter_metadata_options_imds_enabled(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
}