improve proxy documentation

Fixes #507

docs/full-configuration.md

@@ -59,8 +59,8 @@ The configuration file contains the following sections:
   - `temp_path`, string. Defines the path for temporary files such as those used for atomic uploads or file pipes. If you set this option you must make sure that the defined path exists, is accessible for writing by the user running SFTPGo, and is on the same filesystem as the users home directories otherwise the renaming for atomic uploads will become a copy and therefore may take a long time. The temporary files are not namespaced. The default is generally fine. Leave empty for the default.
   - `proxy_protocol`, integer. Support for [HAProxy PROXY protocol](https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt). If you are running SFTPGo behind a proxy server such as HAProxy, AWS ELB or NGNIX, you can enable the proxy protocol. It provides a convenient way to safely transport connection information such as a client's address across multiple layers of NAT or TCP proxies to get the real client IP address instead of the proxy IP. Both protocol versions 1 and 2 are supported. If the proxy protocol is enabled in SFTPGo then you have to enable the protocol in your proxy configuration too. For example, for HAProxy, add `send-proxy` or `send-proxy-v2` to each server configuration line. The following modes are supported:
     - 0, disabled
-    - 1, enabled. Proxy header will be used and requests without proxy header will be accepted
-    - 2, required. Proxy header will be used and requests without proxy header will be rejected
+    - 1, enabled. If the upstream IP is not allowed to send a proxy header the header be ignored. Using this mode does not mean that we can accept connections with and without the proxy header. We always try to read the proxy header and we ignore it if the upstream IP is not allowed to send a proxy header
+    - 2, required. If the upstream IP is not allowed to send a proxy header the connection will be rejected
   - `proxy_allowed`, List of IP addresses and IP ranges allowed to send the proxy header:
     - If `proxy_protocol` is set to 1 and we receive a proxy header from an IP that is not in the list then the connection will be accepted and the header will be ignored
     - If `proxy_protocol` is set to 2 and we receive a proxy header from an IP that is not in the list then the connection will be rejected
@@ -111,12 +111,12 @@ The configuration file contains the following sections:
   - `bindings`, list of structs. Each struct has the following fields:
     - `port`, integer. The port used for serving FTP requests. 0 means disabled. Default: 0.
     - `address`, string. Leave blank to listen on all available network interfaces. Default: "".
-    - `apply_proxy_config`, boolean. If enabled the common proxy configuration, if any, will be applied. Default `true`.
+    - `apply_proxy_config`, boolean. If enabled the common proxy configuration, if any, will be applied. Please note that we expect the proxy header on control and data connections. Default `true`.
     - `tls_mode`, integer. 0 means accept both cleartext and encrypted sessions. 1 means TLS is required for both control and data connection. 2 means implicit TLS. Do not enable this blindly, please check that a proper TLS config is in place if you set `tls_mode` is different from 0.
     - `force_passive_ip`, ip address. External IP address to expose for passive connections. Leavy empty to autodetect. If not empty, it must be a valid IPv4 address. Defaut: "".
     - `client_auth_type`, integer. Set to `1` to require a client certificate and verify it. Set to `2` to request a client certificate during the TLS handshake and verify it if given, in this mode the client is allowed not to send a certificate. At least one certification authority must be defined in order to verify client certificates. If no certification authority is defined, this setting is ignored. Default: 0.
     - `tls_cipher_suites`, list of strings. List of supported cipher suites for TLS version 1.2. If empty, a default list of secure cipher suites is used, with a preference order based on hardware performance. Note that TLS 1.3 ciphersuites are not configurable. The supported ciphersuites names are defined [here](https://github.com/golang/go/blob/master/src/crypto/tls/cipher_suites.go#L52). Any invalid name will be silently ignored. The order matters, the ciphers listed first will be the preferred ones. Default: empty.
-    - `passive_connections_security`, integer. Defines the security checks for passive data connections. Set to `0` to require matching peer IP addresses of control and data connection. Set to `1` to disable any checks. Please note that if you run the FTP service behind a proxy you must enable the proxy protocol for both control and data connections. Default: `0`.
+    - `passive_connections_security`, integer. Defines the security checks for passive data connections. Set to `0` to require matching peer IP addresses of control and data connection. Set to `1` to disable any checks. Please note that if you run the FTP service behind a proxy you must enable the proxy protocol for control and data connections. Default: `0`.
     - `active_connections_security`, integer. Defines the security checks for active data connections. The supported values are the same as described for `passive_connections_security`. Please note that disabling the security checks you will make the FTP service vulnerable to bounce attacks on active data connections, so change the default value only if you are on a trusted/internal network. Default: `0`.
     - `debug`, boolean. If enabled any FTP command will be logged. This will generate a lot of logs. Enable only if you are investigating a client compatibility issue or something similar. You shouldn't leave this setting enabled for production servers. Default `false`.
   - `banner`, string. Greeting banner displayed when a connection first comes in. Leave empty to use the default banner. Default `SFTPGo <version> ready`, for example `SFTPGo 1.0.0-dev ready`.