feat: implement challenge registry (#607)

* feat: implement challenge method registry

This paves the way for implementing a no-js check method (#95) by making
the challenge providers more generic.

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(lib/challenge): rename proof-of-work package to proofofwork

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(lib): make validated challenges a CounterVec

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(lib): annotate jwts with challenge method

Signed-off-by: Xe Iaso <me@xeiaso.net>

* test(lib/challenge/proofofwork): implement tests

Signed-off-by: Xe Iaso <me@xeiaso.net>

* test(lib): add smoke tests for known good and known bad config files

Signed-off-by: Xe Iaso <me@xeiaso.net>

* docs: update CHANGELOG

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(lib): use challenge.Impl#Issue when issuing challenges

Signed-off-by: Xe Iaso <me@xeiaso.net>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/challenge/challenge.go

@@ -0,0 +1,47 @@
+package challenge
+
+import (
+	"log/slog"
+	"net/http"
+	"sort"
+	"sync"
+
+	"github.com/TecharoHQ/anubis/lib/policy"
+	"github.com/a-h/templ"
+)
+
+var (
+	registry map[string]Impl = map[string]Impl{}
+	regLock  sync.RWMutex
+)
+
+func Register(name string, impl Impl) {
+	regLock.Lock()
+	defer regLock.Unlock()
+
+	registry[name] = impl
+}
+
+func Get(name string) (Impl, bool) {
+	regLock.RLock()
+	defer regLock.RUnlock()
+	result, ok := registry[name]
+	return result, ok
+}
+
+func Methods() []string {
+	regLock.RLock()
+	defer regLock.RUnlock()
+	var result []string
+	for method := range registry {
+		result = append(result, method)
+	}
+	sort.Strings(result)
+	return result
+}
+
+type Impl interface {
+	Fail(w http.ResponseWriter, r *http.Request) error
+	Issue(r *http.Request, lg *slog.Logger, rule *policy.Bot, challenge string, ogTags map[string]string) (templ.Component, error)
+	Validate(r *http.Request, lg *slog.Logger, rule *policy.Bot, challenge string) error
+}