When I attempted that...

ROUTINE ZAUTHENTICATE
ZAUTHENTICATE(ServiceName,Namespace,Username,Password,Credentials,Properties) PUBLIC {

#include %occErrors
  
#include %sySecurity
 
 //Make sure we have an error trap to handle unexpected errors
 s $ZT="Error"
 s Name=$zcvt(Username,"U")
 s Name=$p(Username,"@",1)
 s UserRecord=$g(^USERS(Name))
 i UserRecord="" q $SYSTEM.Status.Error($$$UserDoesNotExist,Username)
 d $System.Security.Users.ImpersonateUser()
 s $ZE="No ZAUTHENTICATE routine found" g Error
 q $SYSTEM.Status.OK()
Error //Handle any COS errors here
 s $zt=""
 q $SYSTEM.Status.Error(5002 /*$$$CacheError*/,$ze)
 }
GetCredentials(ServiceName,Namespace,Username,Password,Credentials) Public {
#include %occErrors
#include %sySecurity
#include %sySite
#include %syLDAP
#include %occErrors    
    
    Quit $SYSTEM.Status.Error($$$GetCredentialsFailed)

}
#include %occErrors
#include %sySecurity
#include %sySite
#include %syLDAP
#include %occErrors
#define LDAPServer $Get(^OSUMCLDAP("Server"))
#define WindowsLDAPServer 1
#define WindowsCacheClient 0
#define UseSecureConnection 1
#define UnixCertificateFile ##class(%Library.File).ManagerDirectory()_"LDAPKeyStore/ProdAll.pem"
#define WindowsBaseDN "dc="_$Get(^OSUMCLDAP("Domain"))_",dc=edu"
#define WindowsFilter "sAMAccountname"
#define WindowsAttributeList $lb("displayName","department","mail")

 w !,"Initializing LDAP connection to "_$$$LDAPServer,!
 Read !,"Username: ",Username
 Read !,"Password: ",Password
 
 //Make sure we have an error trap to handle unexpected errors
 s $zt="Error"
 
 s Status = 0
 i Password="" {
         s Status = $SYSTEM.Status.Error($$$UserInvalidPassword)
        g Error
 }

 i $$$WindowsLDAPServer{
    s AdminDN="CN="_$Get(^OSUMCLDAP("User"))_",OU=Authentication Accounts,DC="_$Get(^OSUMCLDAP("Domain"))_",DC=edu"
    s AdminPW=$Get(^OSUMCLDAP("Pass"))
 }
 
 #;The following line sets up the internal LDAP structures. 
 i $$$ISWINDOWS,$$$UseSecureConnection {
    s LD=##Class(%SYS.LDAP).Init($$$LDAPServer,$$$LDAPPORT)
 } else {
     s LD=##Class(%SYS.LDAP).Init($$$LDAPServer)
 }

 i LD=0 {
    s Status=##Class(%SYS.LDAP).GetLastError()
    s Status="Init error: "_Status_" - "_##Class(%SYS.LDAP).Err2String(Status)
    g Error
 }
 s Status=##Class(%SYS.LDAP).SetOption(LD,$$$LDAPOPTXTLSCACERTFILE,$$$UnixCertificateFile)
 i Status'=$$$LDAPSUCCESS{
     s Status ="ldap_SetOption(Certificate) error: "_Status_" - "_##Class(%SYS.LDAP).Err2String(Status) 
     #;w Status,!
     g Error
 }.....

I am getting the following error when I attempt to use my AD account...

If I change Quit $SYSTEM.Status as OK instead of ERROR I get a SYSTEM UNAVAILABLE message.

The issue was that I was trying to call GetCredentials within the ZAUTHENTICATE{}, if I move GetCredentials outside of }, the Delegation Authentication no longer works and I get...

its sort of like...

ZAUTHENTICATE(ServiceName,Namespace,Username,Password,Credentials,Properties) PUBLIC {

#include %occErrors
#include %sySecurity
#include %sySite
#include %syLDAP
#include %occErrors....

}

GetCredentials(ServiceName,Namespace,Username,Password,Credentials) Public {

  // For console sessions, authenticate as _SYSTEM.
  If ServiceName="%Service_Console" {
    Set Username="_SYSTEM"
    Set Password="SYS"
    Quit $SYSTEM.Status.OK()
  }

  // For a web application, authenticate as AdminUser.
  If $isobject($get(%request)) { 
    If %request.Application="/csp/samples/" {
      Set Username="AdminUser"
      Set Password="Test"
      Quit $System.Status.OK()
    }

  }

  // For bindings connections, use regular prompting.
  If ServiceName="%Service_Bindings" {
    Quit $SYSTEM.Status.Error($$$GetCredentialsFailed)
  }  // For all other connections, deny access.
  Quit $SYSTEM.Status.Error($$$AccessDenied)
}

When GetCredentials is called I want it to use the code in ZAUTHENTICATE, so what is the proper format or order that this needs to be done to make this happen...

Thanks for the suggestion. 

I was able to find the following error...

ERROR #9404: Unexpected field in input, LastName, using class base mapping.

It shouldn't matter the order in which the Object Class was defined would it?

as my Base class references another Class

class User.REST.Epic.Msg.GetPatientLocationResponse Extends (Ens.Response, %JSON.Adaptor)
{
Property Results As list Of User.REST.Epic.dt.Response;
}

Class User.REST.Epic.dt.Response Extends (%SerialObject, %XML.Adaptor, %JSON.Adaptor)
{
Property AppointmentSchedules As User.REST.Epic.dt.ArrayOfScheduleProviderReturn(%JSONFIELDNAME = "AppointmentSchedules");
Property AttendingPhysicians As User.REST.Epic.dt.ArrayOfAttendingPhysician(%JSONFIELDNAME = "AttendingPhysicians");
Property CareTeamPCPs As User.REST.Epic.dt.ArrayOfCareTeamPCP(%JSONFIELDNAME = "CareTeamPCPs");
Property ChargeSlipNumber As %String(%JSONFIELDNAME = "ChargeSlipNumber", MAXLEN = "");
Property DateOfBirth As %String(%JSONFIELDNAME = "DateOfBirth", MAXLEN = "");
Property DepartmentIDs As User.REST.Epic.dt.ArrayOfIDType(%JSONFIELDNAME = "DepartmentIDs");
Property EncounterDate As %String(%JSONFIELDNAME = "EncounterDate", MAXLEN = "");
Property FacilityIDs As User.REST.Epic.dt.ArrayOfIDType(%JSONFIELDNAME = "FacilityIDs");
Property FirstName As %String(%JSONFIELDNAME = "FirstName", MAXLEN = "");
Property HospitalAccountIDs As User.REST.Epic.dt.ArrayOfIDType(%JSONFIELDNAME = "HospitalAccountIDs");
Property HospitalService As %String(%JSONFIELDNAME = "HospitalService", MAXLEN = "");
Property LastName As %String(%JSONFIELDNAME = "LastName", MAXLEN = "");
Property MiddleName As %String(%JSONFIELDNAME = "MiddleName", MAXLEN = "");
Property PatientClass As %String(%JSONFIELDNAME = "PatientClass", MAXLEN = "");
Property PatientPhoneNumbers As User.REST.Epic.dt.ArrayOfPhone(%JSONFIELDNAME = "PatientPhoneNumbers");
Property ProviderTeams As User.REST.Epic.dt.ArrayOfProviderTeam(%JSONFIELDNAME = "ProviderTeams");
Property Sex As %String(%JSONFIELDNAME = "Sex", MAXLEN = "");
}

and in User.REST.Epic.dt.Response definitely does not have LastName listed first, but in the JSON result I am seeing it listed as the first Property.

{"LastName":.......}

@Ashok Kumar 
So, I tried...

 set tSC = ..Adapter.SendFormDataArray(.tHTTPResposne,"POST",tHTTPRequest,,,tURL)
 set pResponse = ##class(User.REST.Epic.Msg.GetPatientLocationResponse).%New()
 set dynObject = {}.%FromJSON(tHTTPResposne.Data)
 do pResponse.%JSONImport(dynObject)

set tSC = ..Adapter.SendFormDataArray(.tHTTPResposne,"POST",tHTTPRequest,,,tURL)
set pResponse = ##class(User.REST.Epic.Msg.GetPatientLocationResponse).%New()
do pResponse.%JSONImport(tHTTPResposne.Data)

Not sure I follow... I do all the SetHeader lines, then call  Do tHTTPRequest.EntityBody.Write() is that not writting the headers to tHTTPRequest?

    do tHTTPRequest.EntityBody.Write()
    do tHTTPRequest.OutputHeaders()
    set tURL= "/../../../../"  //..Adapter.URL
    set jsonRequest = {"........."}
    SET tSC = tHTTPRequest.EntityBody.Write(jsonRequest.%ToJSON())
    set tHTTPResposne = ##class(%Net.HttpResponse).%New()
    do tHTTPRequest.OutputParams()
    set tSC = ..Adapter.SendFormDataArray(.tHTTPResposne,"POST",,,tHTTPRequest)

Does the error mean that I can't do just a POST, I need to use SendFormArray?

Here is my Test code...

I enabled DEBUG = 2 on EnsLib.HTTP.OutboundAdapter, but I am still not seeing the entire Request message being sent within the Foreground display that pops up when I execute the Test. 

I was able to $$$LOGINFO(tHTTPRequest.OutputHeaders()) and verified that the header segment is being sent, but it is still throwing a 403 Forbidden error back at me.

I have tried that but still unable to see the Request or Response being sent...

Class User.REST.Epic.EpicOperation Extends (EnsLib.REST.Operation, Ens.Util.JSON)

{

Parameter DEBUG As %Integer = 2;

Parameter INVOCATION = "Queue";

Method getPatientLocationRequest(pRequest As User.REST.Epic.Msg.GetPatientLocationRequest, Output pResponse As EnsLib.HTTP.GenericMessage) As %Status

{

    set tSC = $$$OK

    try{

      set tHTTPRequest = ##class(%Net.HttpRequest).%New()

      do tHTTPRequest.SetHeader("Epic-Client-ID","ed7ca30e-c16a-4053-9233-bff4f5661bb4")

      $$$TRACE("HttpRequest: "_tHTTPRequest) <this returns me just a pointer 8@%Net.HttpRequest>

      set tRequest = ##class(%DynamicObject).%New()

      set tRequest.PatientID = pRequest.PatientID

      set tRequest.PatientIDType = pRequest.PatientIDType

      set tRequest.ContactID = pRequest.ContactID

      set tRequest.ContactIDType = pRequest.ContactIDType

      set tRequest.UserID = pRequest.UserID

      set tRequest.UserIDType = pRequest.UserIDType

      set reqMsg = tHTTPRequest.EntityBody.Write(tRequest)

      $$$TRACE("reqMsg: "_reqMsg)

      set tSC = tHTTPRequest.EntityBody.Write(tRequest.%ToJSON())

      set tURL = ..Adapter.URL

      set tSC = ..Adapter.Post(tURL)

      set stream = "".....

The issue was with the Custom Header field I needed for connecting to Epic.

IRIS

I am able to call the API without any issues using POSTMAN using the same username/password.

I am not sure I understand... I was using the example that was provided in the documentation.

https://docs.intersystems.com/healthconnectlatest/csp/docbook/DocBook.UI.Page.cls?KEY=EREST_operation#EREST_operation_json

If I have to have a Custom Header do I not have to define in this case the Client ID as part of the %DynamicObject?

    set tRequest = ##class(%DynamicAbstractObject).%New()

    set tRequest.clientID = "Epic-Client-ID = xxxxxxxx"

if I am using a Request Class Structure (osuwmc.Epic.Access.Request.GetPatientLocationByVisit2JsonRequest) isn't the set tRequest.payload = pRequest line correct?