Is there a way to set the host header on a service callout?

[pauliacoletti]

I am trying to use a ServiceCallout policy to call an API, and I want to set my own host header. No matter what I try, the edge always overwrites my host header before sending the request so the backend never gets my custom value.

I tried to set the headers in the ServiceCallout policy:

<Request clearPayload="true">
     <IgnoreUnresolvedVariables>false</IgnoreUnresolvedVariables>
     <Set>
         <Headers>
             <Header name="host">foobar.com</Header>
         </Headers>
     </Set>
</Request>

We are able to set this header on a target endpoint be doing an AssignMessage:

<AssignMessage async="false" continueOnError="false" enabled="true" name="HostHeader">
    <DisplayName>HostHeader</DisplayName>
    <Properties/>
    <AssignVariable>
        <Name>target.header.host</Name>
        <Value>foobar.com</Value>
    </AssignVariable>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
</AssignMessage>

But a similar method does not work for ServiceCallout:

<AssignMessage async="false" continueOnError="false" enabled="true" name="calloutRequest">
    <DisplayName> calloutRequest </DisplayName>
    <AssignTo createNew="true" type="request">calloutRequest</AssignTo>
    <Set>
        <Verb>GET</Verb>
	<Headers>
		<Header name="host">foobar.com</Header>
	</Headers>
    </Set>
</AssignMessage>


<AssignMessage async="false" continueOnError="false" enabled="true" name="HostHeader">
    <DisplayName>HostHeader</DisplayName>
    <Properties/>
    <AssignVariable>
        <Name>calloutRequest.header.host</Name>
        <Value>foobar.com</Value>
    </AssignVariable>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
</AssignMessage>


<ServiceCallout async="false" continueOnError="false" enabled="true" name="callout">
    <DisplayName>callout</DisplayName>
    <Properties/>
    <Request clearPayload="true" variable="calloutRequest"/>
    <Response>calloutResponse</Response>
    <HTTPTargetConnection>
        <Properties/>
        <URL>https://postman-echo.com/get</URL>
    </HTTPTargetConnection>
</ServiceCallout>

Is there a way to make sure my host header value makes it to the backend of a ServiceCallout?