Add GitHub Copilot provider

[notlikejuice]

Summary

• add githubcopilot provider configuration
• allow login via fetchGithubCopilotApiKey
• call provider-specific login in CLI

Testing

• pnpm build
• pnpm test (fails: raw-exec-process-group.test.ts)

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https://chatgpt.com/codex/tasks/task_e_684f237b111083268d65d4f2fd75eac8

[Copilot]

Pull Request Overview

This PR introduces a new GitHub Copilot provider configuration and integrates a corresponding API key retrieval function into the CLI login flow.

• Added a new "githubcopilot" provider configuration in providers.ts
• Implemented fetchGithubCopilotApiKey in get-api-key.tsx to support GitHub Copilot token retrieval
• Incorporated provider-specific API key fetching in cli.tsx for login functionality

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
codex-cli/src/utils/providers.ts	Added configuration for the GitHub Copilot provider
codex-cli/src/utils/get-api-key.tsx	Introduced the fetchGithubCopilotApiKey function for retrieving the GitHub Copilot token
codex-cli/src/cli.tsx	Updated the CLI login flow to include provider-specific key fetching for GitHub Copilot

[Copilot]

The logic for fetching the API key for the GitHub Copilot provider is repeated in separate conditional blocks (lines 332-336 and 349-352). Consider refactoring this into a single helper function that handles provider-specific API key retrieval to improve maintainability.

Suggested change

	if (provider.toLowerCase() === "githubcopilot") {
	apiKey = await fetchGithubCopilotApiKey();
	} else {
	apiKey = await fetchApiKey(client.issuer, client.client_id);
	}
	apiKey = await getApiKeyForProvider(provider, client.issuer, client.client_id);