feat: add ability to authenticate using env variable

Fixes zbirenbaum#316

Author: AntoineGS

README.md

@@ -22,8 +22,23 @@ use { "zbirenbaum/copilot.lua" }
 
 ### Authentication
 
+You can authenticate using one of the following methods:
+
+#### Permanent sign-in (Recommended)
+
 Once copilot is running, run `:Copilot auth` to start the authentication process.
 
+#### Token
+
+Get a token from the github cli using:
+
+```sh
+gh auth token
+```
+
+Set either the environment variable `GITHUB_COPILOT_TOKEN` or `GH_COPILOT_TOKEN` to that token.
+Note that if you have the variable set, even empty, the LSP will attempt to use it to log in.
+
 ## Setup and Configuration
 
 You have to run the `require("copilot").setup(options)` function in order to start Copilot.

lua/copilot/init.lua

@@ -3,6 +3,7 @@ local config = require("copilot.config")
 local highlight = require("copilot.highlight")
 local logger = require("copilot.logger")
 local client = require("copilot.client")
+local auth = require("copilot.auth")
 
 local create_cmds = function()
   vim.api.nvim_create_user_command("CopilotDetach", function()
@@ -47,6 +48,12 @@ M.setup = function(opts)
   -- logged here to ensure the logger is setup
   logger.debug("active LSP config (may change runtime):", client.config)
 
+  local token_env_set = (os.getenv("GITHUB_COPILOT_TOKEN") ~= nil) or (os.getenv("GH_COPILOT_TOKEN") ~= nil)
+
+  if token_env_set then
+    auth.signin()
+  end
+
   M.setup_done = true
 end