[cache] Show better error for no write cache (#2084)

## Summary

Show link to configure cache if user is logged in but has no write
cache.

## How was it tested?

<img width="957" alt="image"
src="https://github.com/jetify-com/devbox/assets/544948/5933192f-3cef-49c1-81a5-bbe35c0bacf3">

Author: mikeland73

internal/build/build.go

@@ -91,3 +91,10 @@ func SuccessRedirect() string {
 func Audience() []string {
 	return []string{"https://api.jetpack.io"}
 }
+
+func DashboardHostname() string {
+	if IsDev {
+		return "http://localhost:8080"
+	}
+	return "https://cloud.jetify.com"
+}

internal/devbox/cache.go

@@ -6,6 +6,7 @@ import (
 	"io"
 
 	"go.jetpack.io/devbox/internal/boxcli/usererr"
+	"go.jetpack.io/devbox/internal/build"
 	"go.jetpack.io/devbox/internal/devbox/providers/identity"
 	"go.jetpack.io/devbox/internal/devbox/providers/nixcache"
 	"go.jetpack.io/devbox/internal/nix"
@@ -77,9 +78,19 @@ func getWriteCacheURI(
 	if err != nil {
 		return "", err
 	}
+
 	if len(caches) == 0 {
+		slug, err := identity.GetOrgSlug(ctx)
+		if err != nil {
+			return "", err
+		}
 		return "",
-			usererr.New("You don't have permission to write to any Nix caches.")
+			usererr.New(
+				"You don't have permission to write to any Nix caches. To configure cache, go to "+
+					"%s/teams/%s/devbox",
+				build.DashboardHostname(),
+				slug,
+			)
 	}
 	if len(caches) > 1 {
 		ux.Fwarning(w, "Multiple caches available, using %s.\n", caches[0].GetUri())

internal/devbox/providers/identity/identity.go

@@ -2,8 +2,11 @@ package identity
 
 import (
 	"context"
+	"errors"
 	"os"
 
+	"github.com/go-jose/go-jose/v4"
+	"github.com/go-jose/go-jose/v4/jwt"
 	"go.jetify.com/typeid"
 	"go.jetpack.io/devbox/internal/build"
 	"go.jetpack.io/pkg/api"
@@ -91,3 +94,26 @@ func getAccessTokenFromAPIToken(
 
 	return cachedAccessTokenFromAPIToken, nil
 }
+
+func GetOrgSlug(ctx context.Context) (string, error) {
+	tok, err := GenSession(ctx)
+	if err != nil {
+		return "", err
+	}
+
+	if tok.IDToken == "" {
+		return "", errors.New("ID token is not present")
+	}
+
+	jwt, err := jwt.ParseSigned(tok.IDToken, []jose.SignatureAlgorithm{jose.RS256})
+	if err != nil {
+		return "", err
+	}
+
+	claims := map[string]any{}
+	if err = jwt.UnsafeClaimsWithoutVerification(&claims); err != nil {
+		return "", err
+	}
+
+	return claims["org_trusted_metadata"].(map[string]any)["slug"].(string), nil
+}