This script fetches all of the projects in a Jira Cloud instance. It then fetches all of the project roles for that project, and finally fetches all of the users in that role for that project. In this way, it iterates through the projects and returns information about the users in the project roles.

import groovy.json.JsonSlurper

def sb = []
//Define a string buffer to hold the results

def getUsers = get("/rest/api/2/project")
  .header('Content-Type', 'application/json')
  .asJson()
//Get the list of projects in the instance

def content = getUsers.properties.rawBody
//Get the raw body contents of the HTTP response

def scanner = new java.util.Scanner(content).useDelimiter("\\A")
String rawBody = scanner.hasNext() ? scanner.next() : ""
def json = new JsonSlurper().parseText(rawBody)
//Turn the raw body contents into JSON

json.each{ project ->
//Iterate through the projects
  
  sb.add("$project.name")

  def getRoles = get("/rest/api/2/project/$project.id/role")
    .header('Content-Type', 'application/json')
    .asObject(Map)
//For each project, get the list of roles


  getRoles.body.each{ projectRole ->
  //Iterate through the project roles

      def getRoleMembers = get("$projectRole.value")
      .header('Content-Type', 'application/json')
      .asObject(Map)
      //Return the details about each role

    getRoleMembers.body.actors.each{ roleMember ->
    //Get all the actors (users) in that role

        sb.add("$getRoleMembers.body.name:   $roleMember.displayName")
    }
  }
}

return sb
//Return the results