Rakesh/support device auth (#3531)

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# test

```
codex-rs % export CODEX_DEVICE_AUTH_BASE_URL=http://localhost:3007
codex-rs % cargo run --bin codex login --experimental_use-device-code
   Compiling codex-login v0.0.0 (/Users/rakesh/code/codex/codex-rs/login)
   Compiling codex-mcp-server v0.0.0 (/Users/rakesh/code/codex/codex-rs/mcp-server)
   Compiling codex-tui v0.0.0 (/Users/rakesh/code/codex/codex-rs/tui)
   Compiling codex-cli v0.0.0 (/Users/rakesh/code/codex/codex-rs/cli)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 2.90s
     Running `target/debug/codex login --experimental_use-device-code`
To authenticate, enter this code when prompted: 6Q27-KBVRF with interval 5
^C

```

The error in the last line is since the poll endpoint is not yet
implemented

codex-rs/cli/src/login.rs

@@ -6,6 +6,7 @@ use codex_core::auth::logout;
 use codex_core::config::Config;
 use codex_core::config::ConfigOverrides;
 use codex_login::ServerOptions;
+use codex_login::run_device_code_login;
 use codex_login::run_login_server;
 use codex_protocol::mcp_protocol::AuthMode;
 use std::path::PathBuf;
@@ -55,6 +56,32 @@ pub async fn run_login_with_api_key(
     }
 }
 
+/// Login using the OAuth device code flow.
+pub async fn run_login_with_device_code(
+    cli_config_overrides: CliConfigOverrides,
+    issuer_base_url: Option<String>,
+    client_id: Option<String>,
+) -> ! {
+    let config = load_config_or_exit(cli_config_overrides);
+    let mut opts = ServerOptions::new(
+        config.codex_home,
+        client_id.unwrap_or(CLIENT_ID.to_string()),
+    );
+    if let Some(iss) = issuer_base_url {
+        opts.issuer = iss;
+    }
+    match run_device_code_login(opts).await {
+        Ok(()) => {
+            eprintln!("Successfully logged in");
+            std::process::exit(0);
+        }
+        Err(e) => {
+            eprintln!("Error logging in with device code: {e}");
+            std::process::exit(1);
+        }
+    }
+}
+
 pub async fn run_login_status(cli_config_overrides: CliConfigOverrides) -> ! {
     let config = load_config_or_exit(cli_config_overrides);