remove unnecessary LRU for internode auth token (#20119)

removes contentious usage of mutexes in LRU, which
were never really reused in any manner; we do not
need it.

To trust hosts, the correct way is TLS certs; this PR completely
removes this dependency, which has never been useful.

```
0  0%  100%  25.83s 26.76%  github.com/hashicorp/golang-lru/v2/expirable.(*LRU[...])
0  0%  100%  28.03s 29.04%  github.com/hashicorp/golang-lru/v2/expirable.(*LRU[...])
```

Bonus: use `x-minio-time` as a nanosecond to avoid unnecessary
parsing logic of time strings instead of using a more
straightforward mechanism.

internal/grid/debug.go

@@ -169,13 +169,13 @@ func dummyRequestValidate(r *http.Request) error {
 	return nil
 }
 
-func dummyTokenValidate(token, audience string) error {
-	if token == audience {
+func dummyTokenValidate(token string) error {
+	if token == "debug" {
 		return nil
 	}
-	return fmt.Errorf("invalid token. want %s, got %s", audience, token)
+	return fmt.Errorf("invalid token. want empty, got %s", token)
 }
 
-func dummyNewToken(audience string) string {
-	return audience
+func dummyNewToken() string {
+	return "debug"
 }

internal/grid/grid.go

@@ -26,6 +26,7 @@ import (
 	"io"
 	"net"
 	"net/http"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -208,8 +209,8 @@ func ConnectWS(dial ContextDialer, auth AuthFn, tls *tls.Config) func(ctx contex
 			dialer.NetDial = dial
 		}
 		header := make(http.Header, 2)
-		header.Set("Authorization", "Bearer "+auth(""))
-		header.Set("X-Minio-Time", time.Now().UTC().Format(time.RFC3339))
+		header.Set("Authorization", "Bearer "+auth())
+		header.Set("X-Minio-Time", strconv.FormatInt(time.Now().UnixNano(), 10))
 
 		if len(header) > 0 {
 			dialer.Header = ws.HandshakeHeaderHTTP(header)
@@ -225,4 +226,4 @@ func ConnectWS(dial ContextDialer, auth AuthFn, tls *tls.Config) func(ctx contex
 }
 
 // ValidateTokenFn must validate the token and return an error if it is invalid.
-type ValidateTokenFn func(token, audience string) error
+type ValidateTokenFn func(token string) error

internal/grid/manager.go

@@ -245,7 +245,7 @@ func (m *Manager) IncomingConn(ctx context.Context, conn net.Conn) {
 		writeErr(fmt.Errorf("time difference too large between servers: %v", time.Since(cReq.Time).Abs()))
 		return
 	}
-	if err := m.authToken(cReq.Token, cReq.audience()); err != nil {
+	if err := m.authToken(cReq.Token); err != nil {
 		writeErr(fmt.Errorf("auth token: %w", err))
 		return
 	}
@@ -257,10 +257,10 @@ func (m *Manager) IncomingConn(ctx context.Context, conn net.Conn) {
 }
 
 // AuthFn should provide an authentication string for the given aud.
-type AuthFn func(aud string) string
+type AuthFn func() string
 
 // ValidateAuthFn should check authentication for the given aud.
-type ValidateAuthFn func(auth, aud string) string
+type ValidateAuthFn func(auth string) string
 
 // Connection will return the connection for the specified host.
 // If the host does not exist nil will be returned.

internal/grid/msg.go

@@ -262,14 +262,9 @@ type connectReq struct {
 	Token string
 }
 
-// audience returns the audience for the connect call.
-func (c *connectReq) audience() string {
-	return fmt.Sprintf("%s-%d", c.Host, c.Time.Unix())
-}
-
 // addToken will add the token to the connect request.
 func (c *connectReq) addToken(fn AuthFn) {
-	c.Token = fn(c.audience())
+	c.Token = fn()
 }
 
 func (connectReq) Op() Op {