feat(lib): use new challenge creation flow

Previously Anubis constructed challenge strings from request metadata.
This was a good idea in spirit, but has turned out to be a very bad idea
in practice. This new flow reuses the Store facility to dynamically
create challenge values with completely random data.

This is a fairly big rewrite of how Anubis processes challenges. Right
now it defaults to using the in-memory storage backend, but on-disk
(boltdb) and valkey-based adaptors will come soon.

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

lib/challenge/challenge.go

@@ -1,65 +1,11 @@
 package challenge
 
-import (
-	"log/slog"
-	"net/http"
-	"sort"
-	"sync"
+import "time"
 
-	"github.com/TecharoHQ/anubis/lib/policy"
-	"github.com/TecharoHQ/anubis/lib/policy/config"
-	"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 IssueInput struct {
-	Impressum *config.Impressum
-	Rule      *policy.Bot
-	Challenge string
-	OGTags    map[string]string
-}
-
-type ValidateInput struct {
-	Rule      *policy.Bot
-	Challenge string
-}
-
-type Impl interface {
-	// Setup registers any additional routes with the Impl for assets or API routes.
-	Setup(mux *http.ServeMux)
-
-	// Issue a new challenge to the user, called by the Anubis.
-	Issue(r *http.Request, lg *slog.Logger, in *IssueInput) (templ.Component, error)
-
-	// Validate a challenge, making sure that it passes muster.
-	Validate(r *http.Request, lg *slog.Logger, in *ValidateInput) error
+// Challenge is the metadata about a single challenge issuance.
+type Challenge struct {
+	ID         string            `json:"id"`         // UUID identifying the challenge
+	RandomData string            `json:"randomData"` // The random data the client processes
+	IssuedAt   time.Time         `json:"issuedAt"`   // When the challenge was issued
+	Metadata   map[string]string `json:"metadata"`   // Challenge metadata such as IP address and user agent
 }