cmd: prevent commas in header values from being split (#7268)

`pflag.GetStringSlice` treats commas as delimiters, which causes issues
when passing headers whose values contain commas (`X-Robots-Tag:
noindex, nofollow`). These are incorrectly split into multiple headers
and errors out:

- `X-Robots-Tag: noindex`
- ` nofollow`

Switch to `pflag.GetStringArray`, which does not split on commas[1].

Note that this changes behavior for cases where multiple headers were
provided in a single argument with commas (`--header-down "X-Foo:
Bar,X-Bar: Foo"`). Such cases will now be treated as a single header
value. If this breaking change is unacceptable, we will need a smarter
fallback mechanism.

[1] https://github.com/spf13/pflag/pull/90

modules/caddyhttp/reverseproxy/command.go

@@ -75,8 +75,8 @@ For proxying:
 			cmd.Flags().BoolP("insecure", "", false, "Disable TLS verification (WARNING: DISABLES SECURITY BY NOT VERIFYING TLS CERTIFICATES!)")
 			cmd.Flags().BoolP("disable-redirects", "r", false, "Disable HTTP->HTTPS redirects")
 			cmd.Flags().BoolP("internal-certs", "i", false, "Use internal CA for issuing certs")
-			cmd.Flags().StringSliceP("header-up", "H", []string{}, "Set a request header to send to the upstream (format: \"Field: value\")")
-			cmd.Flags().StringSliceP("header-down", "d", []string{}, "Set a response header to send back to the client (format: \"Field: value\")")
+			cmd.Flags().StringArrayP("header-up", "H", []string{}, "Set a request header to send to the upstream (format: \"Field: value\")")
+			cmd.Flags().StringArrayP("header-down", "d", []string{}, "Set a response header to send back to the client (format: \"Field: value\")")
 			cmd.Flags().BoolP("access-log", "", false, "Enable the access log")
 			cmd.Flags().BoolP("debug", "v", false, "Enable verbose debug logs")
 			cmd.RunE = caddycmd.WrapCommandFuncForCobra(cmdReverseProxy)
@@ -182,7 +182,7 @@ func cmdReverseProxy(fs caddycmd.Flags) (int, error) {
 	}
 
 	// set up header_up
-	headerUp, err := fs.GetStringSlice("header-up")
+	headerUp, err := fs.GetStringArray("header-up")
 	if err != nil {
 		return caddy.ExitCodeFailedStartup, fmt.Errorf("invalid header flag: %v", err)
 	}
@@ -204,7 +204,7 @@ func cmdReverseProxy(fs caddycmd.Flags) (int, error) {
 	}
 
 	// set up header_down
-	headerDown, err := fs.GetStringSlice("header-down")
+	headerDown, err := fs.GetStringArray("header-down")
 	if err != nil {
 		return caddy.ExitCodeFailedStartup, fmt.Errorf("invalid header flag: %v", err)
 	}

modules/caddyhttp/staticresp.go

@@ -79,7 +79,7 @@ Response headers may be added using the --header flag for each header field.
 			cmd.Flags().StringP("body", "b", "", "The body of the HTTP response")
 			cmd.Flags().BoolP("access-log", "", false, "Enable the access log")
 			cmd.Flags().BoolP("debug", "v", false, "Enable more verbose debug-level logging")
-			cmd.Flags().StringSliceP("header", "H", []string{}, "Set a header on the response (format: \"Field: value\")")
+			cmd.Flags().StringArrayP("header", "H", []string{}, "Set a header on the response (format: \"Field: value\")")
 			cmd.RunE = caddycmd.WrapCommandFuncForCobra(cmdRespond)
 		},
 	})
@@ -359,7 +359,7 @@ func cmdRespond(fl caddycmd.Flags) (int, error) {
 	}
 
 	// build headers map
-	headers, err := fl.GetStringSlice("header")
+	headers, err := fl.GetStringArray("header")
 	if err != nil {
 		return caddy.ExitCodeFailedStartup, fmt.Errorf("invalid header flag: %v", err)
 	}