tsnet,internal/client/tailscale: resolve OAuth into authkeys in tsnet (#17191)

* tsnet,internal/client/tailscale: resolve OAuth into authkeys in tsnet

Updates #8403.

* internal/client/tailscale: omit OAuth library via build tag

Updates #12614.

Signed-off-by: Naman Sood <mail@nsood.in>

feature/buildfeatures/feature_oauthkey_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_oauthkey
+
+package buildfeatures
+
+// HasOAuthKey is whether the binary was built with support for modular feature "OAuth secret-to-authkey resolution support".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_oauthkey" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasOAuthKey = false

feature/buildfeatures/feature_oauthkey_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_oauthkey
+
+package buildfeatures
+
+// HasOAuthKey is whether the binary was built with support for modular feature "OAuth secret-to-authkey resolution support".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_oauthkey" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasOAuthKey = true