Initial commit.

internal/authproxy/nonce.go

@@ -0,0 +1,34 @@
+package authproxy
+
+import (
+	"sync"
+	"time"
+)
+
+// nonceCache makes hand-off tokens single-use. Entries expire alongside the
+// token they guard, so the map stays tiny (hand-off tokens live 60 seconds).
+type nonceCache struct {
+	mu   sync.Mutex
+	seen map[string]int64
+}
+
+func newNonceCache() *nonceCache {
+	return &nonceCache{seen: make(map[string]int64)}
+}
+
+// use records the nonce and reports whether this was its first use.
+func (c *nonceCache) use(nonce string, exp int64) bool {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	now := time.Now().Unix()
+	for k, v := range c.seen {
+		if v < now {
+			delete(c.seen, k)
+		}
+	}
+	if _, dup := c.seen[nonce]; dup {
+		return false
+	}
+	c.seen[nonce] = exp
+	return true
+}