The reverse proxy header configuration is incorrect, or you are accessing Nextcloud from a trusted proxy. If not, this is a security issue and can allow an attacker to spoof their IP address as visible to the Nextcloud. Further information can be found in the documentation

[bwibo]

The reverse proxy header configuration is incorrect, or you are accessing Nextcloud from a trusted proxy. If not, this is a security issue and can allow an attacker to spoof their IP address as visible to the Nextcloud. Further information can be found in the documentation

[BWibo]

Hey there,

I was facing the same issue. I resolved it by looking up the CIDR of the Docker network and add it to the trusted proxies.

Get Docker Nextcloud network settings:

$ docker network inspect nextcloud_net

[
  {
    "Name": "nextcloud_net",
    "Id": "xxxxxxxxxxxxxxxxxxxxxxxxx",
    "Created": "2022-12-17T12:00:22.955222771+01:00",
    "Scope": "local",
    "Driver": "bridge",
    "EnableIPv6": false,
    "IPAM": {
      "Driver": "default",
      "Options": null,
      "Config": [
        {
          "Subnet": "10.18.0.0/16",
          "Gateway": "10.18.0.1"
        }
      ]
    },
    "ConfigFrom": {
      "Network": ""
    },
    "ConfigOnly": false,
    "Containers": {
      "xxxxxxxxxxxxx": {
        "Name": "nextcloud-cron-1",
        "EndpointID": "xxxxxxxxxxxxxxx",
        "MacAddress": "02:42:ac:13:00:06",
        "IPv4Address": "10.18.0.6/16",
        "IPv6Address": ""
      },
      "xxxxxxxxxxxxxxxxxx": {
        "Name": "nextcloud-caddy-1",
        "EndpointID": "xxxxxxxxxxxxxxxxxx",
        "MacAddress": "02:42:ac:13:00:05",
        "IPv4Address": "10.18.0.5/16",
        "IPv6Address": ""
      },
      ...
      ...
      ...

From this you can get the IP of the Caddy container or the CIDR of the nextcloud subnet.
According to docs both should work as trusted_proxies setting.

It's interesting that your config works. According to docs this setting should only allow IP4, IP6 and CIDR addresses and no domain names.

[BWibo]

Did it work for you @shad00m ?