# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   rds_cluster_iam_authentication_enabled_check
# 
# Description:
#   This control checks whether an Amazon Relational Database Service (RDS) database (DB) cluster has AWS IAM database authentication activated.
# 
# Reports on:
#   AWS::RDS::DBCluster
# 
# Evaluates:
#   AWS CloudFormation, AWS CloudFormation hook
# 
# Rule Parameters:
#   None
# 
# Scenarios:
#   Scenario: 1
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document does not contain any RDS DB cluster resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an RDS DB cluster resource
#       And: 'Engine' provided is not one of 'aurora' or 'aurora-mysql' or 'aurora-postgresql'
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an RDS DB cluster resource
#       And: 'Engine' provided is one of 'aurora' or 'aurora-mysql' or 'aurora-postgresql'
#       And: 'EnableIAMDatabaseAuthentication' has not been provided
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an RDS DB cluster resource
#       And: 'Engine' provided is one of 'aurora' or 'aurora-mysql' or 'aurora-postgresql'
#       And: 'EnableIAMDatabaseAuthentication' has been provided
#       And: 'EnableIAMDatabaseAuthentication' has been set to a value other than bool(true)
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation document or CloudFormation hook document
#       And: The input document contains an RDS DB cluster resource
#       And: 'Engine' provided is one of 'aurora' or 'aurora-mysql' or 'aurora-postgresql'
#       And: 'EnableIAMDatabaseAuthentication' has been provided
#       And: 'EnableIAMDatabaseAuthentication' has been set to bool(true)
#      Then: PASS

#
# Constants
#
let RDS_DB_CLUSTER_TYPE = "AWS::RDS::DBCluster"
let SUPPORTED_DB_CLUSTER_ENGINES = ["aurora", "aurora-mysql","aurora-postgresql"]
let INPUT_DOCUMENT = this

#
# Assignments
#
let db_clusters = Resources.*[ Type == %RDS_DB_CLUSTER_TYPE ]

#
# Primary Rules
#
rule rds_cluster_iam_authentication_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                                       %db_clusters not empty {
    check(%db_clusters.Properties)
        <<
        [CT.RDS.PR.4]: Require an Amazon RDS database cluster to have AWS IAM database authentication configured
        [FIX]: Set 'EnableIAMDatabaseAuthentication' to 'true'.
        >>
}

rule rds_cluster_iam_authentication_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %RDS_DB_CLUSTER_TYPE) {
    check(%INPUT_DOCUMENT.%RDS_DB_CLUSTER_TYPE.resourceProperties)
        <<
        [CT.RDS.PR.4]: Require an Amazon RDS database cluster to have AWS IAM database authentication configured
        [FIX]: Set 'EnableIAMDatabaseAuthentication' to 'true'.
        >>
}

rule check(db_cluster) {
    %db_cluster [
        # Scenario 2
        filter_engine(this)
    ] {
       # Scenario 3
       EnableIAMDatabaseAuthentication exists
       # Scenario 4 and 5
       EnableIAMDatabaseAuthentication == true
    }
}

rule filter_engine(cluster_properties) {
    %cluster_properties {
        Engine exists
        Engine in %SUPPORTED_DB_CLUSTER_ENGINES
    }
}

#
# 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
}