context: add CONTEXT action to apply options on current request

lib/action/proxy.go

@@ -0,0 +1,80 @@
+package action
+
+import (
+	"fmt"
+	"git.gammaspectra.live/git/go-away/lib/challenge"
+	"git.gammaspectra.live/git/go-away/lib/policy"
+	"github.com/goccy/go-yaml"
+	"github.com/goccy/go-yaml/ast"
+	"log/slog"
+	"net/http"
+	"regexp"
+)
+
+func init() {
+	Register[policy.RuleActionPROXY] = func(state challenge.StateInterface, ruleName, ruleHash string, settings ast.Node) (Handler, error) {
+		params := ProxyDefaultSettings
+
+		if settings != nil {
+			ymlData, err := settings.MarshalYAML()
+			if err != nil {
+				return nil, err
+			}
+			err = yaml.Unmarshal(ymlData, &params)
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		if params.Match != "" {
+			expr, err := regexp.Compile(params.Match)
+			if err != nil {
+				return nil, err
+			}
+
+			return Proxy{
+				Match:   expr,
+				Rewrite: params.Rewrite,
+				Backend: params.Backend,
+			}, nil
+		}
+
+		return Proxy{
+			Backend: params.Backend,
+		}, nil
+	}
+}
+
+var ProxyDefaultSettings = ProxySettings{}
+
+type ProxySettings struct {
+	Match   string `yaml:"proxy-match"`
+	Rewrite string `yaml:"proxy-rewrite"`
+	Backend string `yaml:"proxy-backend"`
+}
+
+type Proxy struct {
+	Match   *regexp.Regexp
+	Rewrite string
+	Backend string
+}
+
+func (a Proxy) Handle(logger *slog.Logger, w http.ResponseWriter, r *http.Request, done func() (backend http.Handler)) (next bool, err error) {
+	data := challenge.RequestDataFromContext(r.Context())
+
+	backend := data.State.GetBackend(a.Backend)
+	if backend == nil {
+		return false, fmt.Errorf("backend for %s not found", a.Backend)
+	}
+
+	if a.Match != nil {
+		// rewrite query
+		r.URL.Path = a.Match.ReplaceAllString(r.URL.Path, a.Rewrite)
+	}
+
+	// set headers, ignore reply
+	_ = done()
+	backend.ServeHTTP(w, r)
+
+	return false, nil
+}