HAProxy how to substring path

Question

Given a backend that running on:

172.18.1.125:8888

curl tested:

curl --location --request GET "http://172.18.1.125:8888/oauth/sign-key"
sample_response    //>> HERE IS RESPONSE

I want to config a rule to transform

http://172.18.1.125/api/authorization/oauth/sign-key

to

http://172.18.1.125:8888/oauth/sign-key

Here is my haproxy config:

global
    log         /dev/log local0
    chroot      /var/lib/haproxy
    pidfile     /var/run/haproxy.pid
    maxconn     4000
    debug
    user        haproxy
    group       haproxy
    daemon

    stats socket /var/lib/haproxy/stats
    ssl-default-bind-ciphers PROFILE=SYSTEM
    ssl-default-server-ciphers PROFILE=SYSTEM

defaults
    mode                    http
    log                     global
    option                  httplog
    option                  dontlognull
    option http-server-close
    option forwardfor       except 127.0.0.0/8
    option                  redispatch
    retries                 3
    timeout http-request    10s
    timeout queue           1m
    timeout connect         10s
    timeout client          1m
    timeout server          1m
    timeout http-keep-alive 10s
    timeout check           10s
    maxconn                 3000

frontend api_gateway
    bind :80
    acl PATH_auth path_beg /api/authorization/

    use_backend be_auth if PATH_auth

backend be_auth
    server s1 172.18.1.125:8888
    http-request set-header Host 172.18.1.125

After that I use curl to test my haproxy:

curl --location --request GET "http://172.18.1.125/api/authorization/oauth/sign-key"

I expect that this request will be route to:

http://172.18.1.125:8888/oauth/sign-key

But seems that it route to

http://172.18.1.125:8888/api/authorization/oauth/sign-key

I don't know how to remove /api/authorization from the path. Any answer would be appreciate