V2: Rewrite for Onlyoffice Server

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This is the standard approach for this kind of scenario:

example.com {
  route /ds-vpath/* {
    uri strip_prefix /ds-vpath
    reverse_proxy http://nextcloud_office
  }
  reverse_proxy http://nextcloud_app
}

You can test that Caddy is routing this logic correctly by running this exact Caddyfile:

http://:8080 {
  route /ds-vpath/* {
    uri strip_prefix /ds-vpath
    reverse_proxy localhost:8081
  }
  reverse_proxy localhost:8082
}

http://:8081 {
  respond "8081 {uri}" 200
}

http://:8082 {
  respond "8082 {uri}" 200
}

And I do some quick tests to confirm the expected behaviour:

~/Projects/test
➜ ./caddy version
v2.1.1 h1:X9k1+ehZPYYrSqBvf/ocUgdLSRIuiNiMo7CvyGUQKeA=

~/Projects/test
➜ curl -iL localhost:8080/stuff
HTTP/1.1 200 OK
Content-Length: 11
Date: Mon, 06 Jul 2020 23:29:10 GMT
Server: Caddy
Server: Caddy
Content-Type: text/plain; charset=utf-8

8082 /stuff⏎

~/Projects/test
➜ curl -iL localhost:8080/ds-vpath
HTTP/1.1 200 OK
Content-Length: 14
Date: Mon, 06 Jul 2020 23:29:16 GMT
Server: Caddy
Server: Caddy
Content-Type: text/plain; charset=utf-8

8082 /ds-vpath⏎

~/Projects/test
➜ curl -iL localhost:8080/ds-vpath/
HTTP/1.1 200 OK
Content-Length: 6
Date: Mon, 06 Jul 2020 23:29:18 GMT
Server: Caddy
Server: Caddy
Content-Type: text/plain; charset=utf-8

8081 /⏎

In this manner I have demonstrated that requests to /ds-vpath/ have the prefix stripped before being proxied to a specific upstream, whereas other requests (including /ds-vpath, no trailing slash) are sent to the catch-all upstream.