# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   cloudfront_no_deprecated_ssl_protocols_check
# 
# Description:
#   This control checks whether your Amazon CloudFront distributions are using deprecated SSL protocols for HTTPS communication between CloudFront edge locations and custom origins.
# 
# Reports on:
#   AWS::CloudFront::Distribution
# 
# 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 CloudFront distribution resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a CloudFront distribution resource
#       And: 'Origins' is not present or is an empty list
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a CloudFront distribution resource
#       And: One or more 'Origins' has been configured
#       And: There are no 'Origins' with a 'CustomOriginConfig'
#      Then: SKIP
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a CloudFront distribution resource
#       And: One or more 'Origins' has been configured
#       And: There one or more 'Origins' with a 'CustomOriginConfig'
#       And: All 'Origins' with a 'CustomOriginConfig' have an 'OriginProtocolPolicy' of 'http-only'
#      Then: SKIP
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a CloudFront distribution resource
#       And: 'CustomOrigin' is present on the CloudFront distribution resource
#      Then: FAIL
#   Scenario: 6
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a CloudFront distribution resource
#       And: One or more 'Origins' has been configured
#       And: There one or more 'Origins' with a 'CustomOriginConfig'
#       And: One or more 'Origins' with a 'CustomOriginConfig' have an 'OriginProtocolPolicy' not equal to 'http-only'
#       And: 'OriginSSLProtocols' has not been specified or specified as an empty list
#      Then: FAIL
#   Scenario: 7
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a CloudFront distribution resource
#       And: One or more 'Origins' has been configured
#       And: There one or more 'Origins' with a 'CustomOriginConfig'
#       And: One or more 'Origins' with a 'CustomOriginConfig' have an 'OriginProtocolPolicy' not equal to 'http-only'
#       And: 'OriginSSLProtocols' has been specified as a non-empty list and contains 'SSLv3'
#      Then: FAIL
#   Scenario: 8
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a CloudFront distribution resource
#       And: One or more 'Origins' has been configured
#       And: There one or more 'Origins' with a 'CustomOriginConfig'
#       And: One or more 'Origins' with a 'CustomOriginConfig' have an 'OriginProtocolPolicy' not equal to 'http-only'
#       And: 'OriginSSLProtocols' has been specified as a non-empty list and does not contain 'SSLv3'
#      Then: PASS

#
# Constants
#
let CLOUDFRONT_DISTRIBUTION_TYPE = "AWS::CloudFront::Distribution"
let UNSUPPORTED_ORIGIN_SSL_PROTOCOLS = [ "SSLv3" ]
let OUT_OF_SCOPE_PROTOCOL_POLICIES = [ "http-only" ]
let INPUT_DOCUMENT = this

#
# Assignments
#
let cloudfront_distributions = Resources.*[ Type == %CLOUDFRONT_DISTRIBUTION_TYPE ]

#
# Primary Rules
#
rule cloudfront_no_deprecated_ssl_protocols_check when is_cfn_template(%INPUT_DOCUMENT)
                                                       %cloudfront_distributions not empty {
    check(%cloudfront_distributions.Properties)
        <<
        [CT.CLOUDFRONT.PR.11]: Require an Amazon CloudFront distribution to use updated SSL protocols between edge locations and custom origins
        [FIX]: Remove deprecated SSL protocols from 'OriginSSLProtocols' in 'Origins' that have 'CustomOriginConfig' configurations.
        >>
}

rule cloudfront_no_deprecated_ssl_protocols_check when is_cfn_hook(%INPUT_DOCUMENT, %CLOUDFRONT_DISTRIBUTION_TYPE) {
    check(%INPUT_DOCUMENT.%CLOUDFRONT_DISTRIBUTION_TYPE.resourceProperties)
        <<
        [CT.CLOUDFRONT.PR.11]: Require an Amazon CloudFront distribution to use updated SSL protocols between edge locations and custom origins
        [FIX]: Remove deprecated SSL protocols from 'OriginSSLProtocols' in 'Origins' that have 'CustomOriginConfig' configurations.
        >>
}

#
# Parameterized Rules
#
rule check(cloudfront_distribution) {
    %cloudfront_distribution[
        filter_cloudfront_distribution_with_legacy_origins(this)
    ] {
        DistributionConfig {
            # Scenario 5
            CustomOrigin not exists
        }
    }

    %cloudfront_distribution[
        # Scenario 2
        filter_cloudfront_distribution_with_origins(this)
    ] {
        DistributionConfig {
            Origins [
                # Scenario 3 and 4
                CustomOriginConfig exists
                CustomOriginConfig is_struct
                filter_custom_origin_config(CustomOriginConfig)
            ] {
                CustomOriginConfig {
                    # Scenario 6, 7 and 8
                    OriginSSLProtocols exists
                    OriginSSLProtocols is_list
                    OriginSSLProtocols not empty
                    %UNSUPPORTED_ORIGIN_SSL_PROTOCOLS.* not in OriginSSLProtocols
                }
            }
        }
    }
}


rule filter_cloudfront_distribution_with_origins(cloudfront_distribution) {
    %cloudfront_distribution {
        DistributionConfig exists
        DistributionConfig is_struct

        DistributionConfig {
            Origins exists
            Origins is_list
            Origins not empty
        }
    }
}

rule filter_cloudfront_distribution_with_legacy_origins(cloudfront_distribution) {
    %cloudfront_distribution {
        DistributionConfig exists
        DistributionConfig is_struct

        DistributionConfig {
            CustomOrigin exists
        }
    }
}

rule filter_custom_origin_config(custom_origin_config) {
    %custom_origin_config {
        OriginProtocolPolicy exists
        OriginProtocolPolicy not in %OUT_OF_SCOPE_PROTOCOL_POLICIES
    }
}

#
# 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
}