Cookie Path Defaults to Root '/' Even when Using "proxy-prefix" option

[tuaris]

I'm trying to ad Oauth to an application running in a sub location "http://www.domain.tld/sublocation". I can't run the proxy on the root of the site for technical reasons.

I specify the proxy-prefix to be:

-proxy-prefix /sublocation/oauth2

In the browser, this results in a redirect to:

/sublocation/oauth2/start?rd=%2F

The response header for the cookie is:

set-cookie: _oauth2_proxy=; Path=/; 

The log shows:

2019/01/14 21:13:44 oauthproxy.go:602: 127.0.0.1:35242 Cookie "_oauth2_proxy" not present
127.0.0.1 - - [14/Jan/2019:21:13:44 +0000] www.domain.tld GET - "/oauth2/start?rd=%2F" HTTP/1.1 "Mozilla/5.0 (X11; FreeBSD amd64; rv:62.0) Gecko/20100101 Firefox/62.0" 403 2546 0.000