Get Decrypted Jenkins Credentials via Script Console

decrypt_credentials.groovy

import jenkins.*
import jenkins.model.*
import hudson.*
import hudson.model.*
  
def credId = 'my_credentials_id'
def jenkinsCredentials = com.cloudbees.plugins.credentials.CredentialsProvider.lookupCredentials(
        com.cloudbees.plugins.credentials.Credentials.class,
        Jenkins.instance,
        null,
        null
);
for (creds in jenkinsCredentials) {
  if (creds.id == credId) {
    // may vary because of credential type
    println creds.username
    println creds.password
  }
}