forwardauth: Support renaming copied headers, block support (#4783)

caddytest/integration/caddyfile_adapt/forward_auth_rename_headers.txt

@@ -0,0 +1,116 @@
+:8881
+
+forward_auth localhost:9000 {
+	uri /auth
+	copy_headers A>1 B C>3 {
+		D
+		E>5
+	}
+}
+----------
+{
+	"apps": {
+		"http": {
+			"servers": {
+				"srv0": {
+					"listen": [
+						":8881"
+					],
+					"routes": [
+						{
+							"handle": [
+								{
+									"handle_response": [
+										{
+											"match": {
+												"status_code": [
+													2
+												]
+											},
+											"routes": [
+												{
+													"handle": [
+														{
+															"handler": "headers",
+															"request": {
+																"set": {
+																	"1": [
+																		"{http.reverse_proxy.header.A}"
+																	],
+																	"3": [
+																		"{http.reverse_proxy.header.C}"
+																	],
+																	"5": [
+																		"{http.reverse_proxy.header.E}"
+																	],
+																	"B": [
+																		"{http.reverse_proxy.header.B}"
+																	],
+																	"D": [
+																		"{http.reverse_proxy.header.D}"
+																	]
+																}
+															}
+														}
+													]
+												}
+											]
+										},
+										{
+											"routes": [
+												{
+													"handle": [
+														{
+															"exclude": [
+																"Connection",
+																"Keep-Alive",
+																"Te",
+																"Trailers",
+																"Transfer-Encoding",
+																"Upgrade"
+															],
+															"handler": "copy_response_headers"
+														}
+													]
+												},
+												{
+													"handle": [
+														{
+															"handler": "copy_response"
+														}
+													]
+												}
+											]
+										}
+									],
+									"handler": "reverse_proxy",
+									"headers": {
+										"request": {
+											"set": {
+												"X-Forwarded-Method": [
+													"{http.request.method}"
+												],
+												"X-Forwarded-Uri": [
+													"{http.request.uri}"
+												]
+											}
+										}
+									},
+									"rewrite": {
+										"method": "GET",
+										"uri": "/auth"
+									},
+									"upstreams": [
+										{
+											"dial": "localhost:9000"
+										}
+									]
+								}
+							]
+						}
+					]
+				}
+			}
+		}
+	}
+}

modules/caddyhttp/reverseproxy/forwardauth/caddyfile.go

@@ -17,6 +17,7 @@ package forwardauth
 import (
 	"encoding/json"
 	"net/http"
+	"strings"
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/caddyconfig"
@@ -115,7 +116,7 @@ func parseCaddyfile(h httpcaddyfile.Helper) ([]httpcaddyfile.ConfigValue, error)
 	// collect the headers to copy from the auth response
 	// onto the original request, so they can get passed
 	// through to a backend app
-	headersToCopy := []string{}
+	headersToCopy := make(map[string]string)
 
 	// read the subdirectives for configuring the forward_auth shortcut
 	// NOTE: we delete the tokens as we go so that the reverse_proxy
@@ -141,10 +142,28 @@ func parseCaddyfile(h httpcaddyfile.Helper) ([]httpcaddyfile.ConfigValue, error)
 
 			case "copy_headers":
 				args := dispenser.RemainingArgs()
+				hadBlock := false
+				for nesting := dispenser.Nesting(); dispenser.NextBlock(nesting); {
+					hadBlock = true
+					args = append(args, dispenser.Val())
+				}
+
+				dispenser.Delete() // directive name
+				if hadBlock {
+					dispenser.Delete() // opening brace
+					dispenser.Delete() // closing brace
+				}
+				for range args {
 					dispenser.Delete()
+				}
+
 				for _, headerField := range args {
-					dispenser.Delete()
+					if strings.Contains(headerField, ">") {
-					headersToCopy = append(headersToCopy, headerField)
+						parts := strings.Split(headerField, ">")
+						headersToCopy[parts[0]] = parts[1]
+					} else {
+						headersToCopy[headerField] = headerField
+					}
 				}
 				if len(headersToCopy) == 0 {
 					return nil, dispenser.ArgErr()
@@ -180,9 +199,9 @@ func parseCaddyfile(h httpcaddyfile.Helper) ([]httpcaddyfile.ConfigValue, error)
 			},
 		}
 
-		for _, headerField := range headersToCopy {
+		for from, to := range headersToCopy {
-			handler.Request.Set[headerField] = []string{
+			handler.Request.Set[to] = []string{
-				"{http.reverse_proxy.header." + headerField + "}",
+				"{http.reverse_proxy.header." + from + "}",
 			}
 		}