Flask as proxy for avoiding CORS

In my company we have many HIL modules that provide OpenAPI to perform some basic operation, such as start and stop measurements and download log files or user files.
I am providing a common frontend as a simple web server running flask on apache, hence the devlopers can just connect to the web page, select the HIL and then perform some operations.
As a side note, during the developement I am running Flask on localhost in pycharm, once I have a stable RC I upload on git and sync the server side with GIT.

Up to this moment, in the interface I have two simple buttons: one to retrieve the list of the files that can be downloaded and one to select and download the actual file(s).

The connect button performs a POST request to the flask server via javascript:

function myget(id, cb){
 const xhttp = new XMLHttpRequest
 var data = new URLSearchParams();
 var url = "MiniHILSFunctions";
 var ip = document.getElementById(id).innerHTML;
 var params = 'ip='+ip
 // console.log(ip)
 // console.log(params)
 xhttp.open("POST", url, true)
 xhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
 xhttp.send(params)
 xhttp.onload = () => document.getElementById(cb).innerHTML = xhttp.responseText
}

Then the flask server handles the actual request to the selected HIL server:

@app.route('/MiniHILSFunctions', methods=['POST', 'GET'])
def MiniHilsfunctions(par=None):
    if request.method == 'POST':
        print("request here")
        ip = request.form.get('ip')
        print(ip)
        headers={
            "accept": "text/json"
        }
        url="http://" + ip + "/api/RemoteFiles/Info"
        print(url)
        r = requests.get(url, headers=headers)
        response = r.json()
        print(type(response))
        print(response[0])
        response = jsonify(response)
    else:
        response = "getting data"
    return response, 200, {'Content-Type': 'text/plain'}

returningt the json response to the web interface updating some paragraph to show the json received.

Now, when the user selcts the file I would like to trigger a download of the selected file. The problem here is that the mini hil server issues a CORS error when I try to download a file using javascript, hence I need to ask the flask server to trigger the request instead of the browser.

@app.route('/MiniHILSDownload', methods=['POST', 'GET'])
def MiniHILSDownload(par=None):
    if request.method == 'POST':
        print("request here")
        ip = request.form.get('ip')
        ftype = request.form.get('ftype')
        fname = request.form.get('fname')
        print(ip, " ", ftype, " ", fname)
        if ftype == '1':  # UserFile
            ftype = 'UserFile'
        if ftype == '2':  # LoggingFile
            ftype = 'LoggingFile'
        if ftype == '3':  # Configuration
            ftype = 'Configuration'
        if ftype == '4':  # ReportFile
            ftype = 'ReportFile'

        print(ftype)

        headers={
            "accept": "text/plain",
            "FileType": ftype
        }

        url = r"http://" + ip + r"/api/RemoteFiles/" + fname
        print(url)
        response = requests.get(url, headers=headers)
        # response = r.json()
        print(type(response))
        print(response)
        #response = jsonify(response)

    response = "getting data"
    return ?
    

My issues here are:

1. I don’t want to store any file on the flask server, one approach would be to store the chunks being downloaded to a ram buffer and then:
2. I don’t know how to pass each chunk of the file from the server to the web interface

Any hint would be gladly appreciated.