# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   rds_instance_iam_authentication_enabled_check
# 
# Description:
#   This control checks whether an Amazon RDS database (DB) instance has AWS IAM database authentication activated.
# 
# Reports on:
#   AWS::RDS::DBInstance
# 
# 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 RDS DB instance resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an RDS DB instance resource
#       And: 'Engine' is not in-scope database engines - 'mariadb', 'mysql', 'postgres'
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an RDS DB instance resource
#       And: 'Engine' is in-scope database engines - 'mariadb', 'mysql', 'postgres'
#       And: 'EnableIAMDatabaseAuthentication' has not been specified
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an RDS DB instance resource
#       And: 'Engine' is in-scope database engines - 'mariadb', 'mysql', 'postgres'
#       And: 'EnableIAMDatabaseAuthentication' has been specified
#       And: 'EnableIAMDatabaseAuthentication' has been set to bool(false)
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an RDS DB instance resource
#       And: 'Engine' is in-scope database engines - 'mariadb', 'mysql', 'postgres'
#       And: 'EnableIAMDatabaseAuthentication' has been specified
#       And: 'EnableIAMDatabaseAuthentication' has been set to bool(true)
#      Then: PASS

#
# Constants
#
let RDS_DB_INSTANCE_TYPE = "AWS::RDS::DBInstance"
let INPUT_DOCUMENT = this
let SUPPORTED_RDS_INSTANCE_ENGINES = ["mariadb", "mysql", "postgres"]

#
# Assignments
#
let rds_db_instances = Resources.*[ Type == %RDS_DB_INSTANCE_TYPE ]

#
# Primary Rules
#
rule rds_instance_iam_authentication_enabled_check when is_cfn_template(%INPUT_DOCUMENT)
                                                        %rds_db_instances not empty {
    check(%rds_db_instances.Properties)
        <<
        [CT.RDS.PR.7]: Require Amazon RDS database instances to have AWS IAM authentication configured
        [FIX]: Set 'EnableIAMDatabaseAuthentication' to 'true'.
        >>
}

rule rds_instance_iam_authentication_enabled_check when is_cfn_hook(%INPUT_DOCUMENT, %RDS_DB_INSTANCE_TYPE) {
    check(%INPUT_DOCUMENT.%RDS_DB_INSTANCE_TYPE.resourceProperties)
        <<
        [CT.RDS.PR.7]: Require Amazon RDS database instances to have AWS IAM authentication configured
        [FIX]: Set 'EnableIAMDatabaseAuthentication' to 'true'.
        >>
}

#
# Parameterized Rules
#
rule check(rds_db_instance) {
    %rds_db_instance [filter_engine(this)] {
        #Scenario: 3
        EnableIAMDatabaseAuthentication exists
        #Scenario: 4 and 5
        EnableIAMDatabaseAuthentication == true
    }
}

rule filter_engine(db_properties) {
    %db_properties {
        #Scenario: 2
        Engine exists
        Engine is_string
        Engine in %SUPPORTED_RDS_INSTANCE_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
}