Go-reverseproxy interferes with .net [Authorize] attribute - asp.net

Question

I am running an ASP.NET MVC web application with Vue.js as frontend. For access control management, I am using pritunl-zero, a zero-trust reverse-proxy written in Go.
Locally the app works fine with anonymous authentication but deployed and protected from the proxy every method call that need auth will be denied with 401.0 from the IIS10 web server.
When I remove the proxy from the infrastructure it works.
Protected method call (eg)
[Authorize]
[HttpPut, Route("api/ping"), ResponseType(typeof(WorkflowDto))]
public IHttpActionResult PingWorkflow(WorkflowCommentDto commentDto)
Vue frontend log in console
createError.js:16
Uncaught (in promise) Error: Request failed with status code 401
at e.exports (createError.js:16:15)
at e.exports (settle.js:17:12)
at XMLHttpRequest.O (xhr.js:66:7)
The HTTP-header causing 401 response
GET /api/workflow/ping HTTP/1.1
Accept: */*
Accept-Encoding: gzip, deflate, br
Accept-Language: de,de-DE;q=0.9,en;q=0.8,en-GB;q=0.7,en-US;q=0.6,cy;q=0.5
Cache-Control: no-cache
Connection: keep-alive
Cookie: pritunl-zero=MTY1NzY5OTc0NHxEdEU...
Host: workflow.host.de
Pragma: no-cache
Referer: https://workflow.host.de/
Sec-Fetch-Dest: empty
Sec-Fetch-Mode: cors
Sec-Fetch-Site: same-origin
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/103.0.5060.114 Safari/537.36 Edg/103.0.1264.49
sec-ch-ua: ".Not/A)Brand";v="99", "Microsoft Edge";v="103", "Chromium";v="103"
sec-ch-ua-mobile: ?0
sec-ch-ua-platform: "Windows"
token: 8cf78dcd-3b17-4481-8be3-10821519c23c
The working HTTP-header
:authority: wf.host.de
:method: GET
:path: /api/workflow/Ping
:scheme: https
accept: */*
accept-encoding: gzip, deflate, br
accept-language: de,de-DE;q=0.9,en;q=0.8,en-GB;q=0.7,en-US;q=0.6,cy;q=0.5
cache-control: no-cache
cookie: pritunl-zero=MTY1Nzc3NjkwOHxZTVRUWUF5d0s0c180aTB...; pritunl-zero=MTY1NzgwMTE3MnxlWk9vYkZ2ZGQ0TTdVZmZKODdWb19SRzFSV...
pragma: no-cache
referer: https://wf.host.de/
sec-ch-ua: ".Not/A)Brand";v="99", "Microsoft Edge";v="103", "Chromium";v="103"
sec-ch-ua-mobile: ?0
sec-ch-ua-platform: "Windows"
sec-fetch-dest: empty
sec-fetch-mode: cors
sec-fetch-site: same-origin
token: 8cf78dcd-3b17-4481-8be3-10821519c23c
user-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/103.0.5060.114 Safari/537.36 Edg/103.0.1264.49
The response from server (that one works)
cache-control: no-cache
content-length: 214
content-type: application/json; charset=utf-8
date: Thu, 14 Jul 2022 12:25:09 GMT
expires: -1
pragma: no-cache
server: Microsoft-IIS/10.0
strict-transport-security: max-age=0; includeSubDomains; preload
x-aspnet-version: 4.0.30319
x-powered-by: ASP.NET
Response from server (401)
HTTP/1.1 401 Unauthorized
Cache-Control: no-cache
Content-Length: 61
Content-Type: application/json; charset=utf-8
Date: Wed, 13 Jul 2022 08:09:12 GMT
Expires: -1
Pragma: no-cache
Server: Microsoft-IIS/10.0
X-Aspnet-Version: 4.0.30319
X-Powered-By: ASP.NET
Has anyone any hint how to fix this, that the application can work with the proxy?
What I tried:
New IIS with new site and new deployment
Many web.config settings regarding anonymous authentication
Different configs regarding the application pool
Latest update from pritunl
Thanks in advance for any hint.