ipn/localapi: send Tailscale version in ACME User-Agent (#5499)

Requested by a friend at Let's Encrypt.

Signed-off-by: Andrew Dunham <andrew@tailscale.com>

ipn/localapi/cert.go

@@ -38,6 +38,7 @@ import (
 	"tailscale.com/envknob"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/types/logger"
+	"tailscale.com/version"
 	"tailscale.com/version/distro"
 )
 
@@ -185,7 +186,10 @@ func (h *Handler) getCertPEM(ctx context.Context, logf logger.Logf, traceACME fu
 	if err != nil {
 		return nil, fmt.Errorf("acmeKey: %w", err)
 	}
-	ac := &acme.Client{Key: key}
+	ac := &acme.Client{
+		Key:       key,
+		UserAgent: "tailscaled/" + version.Long,
+	}
 
 	a, err := ac.GetReg(ctx, "" /* pre-RFC param */)
 	switch {

version/version.go

@@ -23,7 +23,8 @@ var Long = ""
 
 // Short is a short version number for this build, of the form
 // "x.y.z" for builds stamped in the usual way (see
-// build_dist.sh in the root) or, for binaries built by hand with the                                                                            // go tool, it's like Long's dev form, but ending at the date part,
+// build_dist.sh in the root) or, for binaries built by hand with the
+// go tool, it's like Long's dev form, but ending at the date part,
 // of the form "1.23.0-dev20220316".
 var Short = ""