Mule application with "Client ID Enforcement Policy" fails when client credentials are encrypted

SYMPTOM

Application is configured to use client id enforcement policy. During this process, environment client_id and client_secret values are encrypted and the application is set to use encrypted client credentials. All the incoming requests to the application that is linked to the Client ID Enforcement Policy, fails to evaluate client_id expression.

Message : "Script 'attributes.headers'client_id' ' has errors:
Invalid input '#', expected ??? (line 1, column 21):
at 1 : 1" evaluating expression: "attributes.headers'client_id'".
Error type : MULE:EXPRESSION
Element : 1170138-client-id-enforcement/source/processors/0/processors/0 @ client-id-enforcement-1170138-testclientpolicyFlow:/Users/schallagulla/Documents/softs/mule-enterprise-standalone-4.2.2/policies/client-id-enforcement-1170138/policy.xml:23
Element XML : <client-id-enforcement:validate-client config-ref="clientEnforcementConfig" clientId="#attributes.headers[&#39;client_id&#39;]" clientSecret="#attributes.headers[&#39;client_secret&#39;]"></client-id-enforcement:validate-client>

Custom Expressions for client_id and client_secret in the policy.

#[attributes.headers['client_id']]
#[attributes.headers['client_secret']]

For steps to encrypt client credentials and how it works, refer to this link. This behavior is seen in 4.2.2 and 4.3.0 runtimes.

CAUSE

SOLUTION