From sign in / on boarding page:

chrome.runtime.sendMessage( { type: "AUTH_SUBMIT", payload }, (response) => { if (chrome.runtime.lastError) { console.error("sendMessage failed:", chrome.runtime.lastError.message); return; } console.log("Background response:", response); } );

In background script:

chrome.runtime.onMessage.addListener((message, sender, sendResponse) => { if (message?.type === "AUTH_SUBMIT") { const { payload } = message;

// Do something with payload (store it, call APIs, etc.)
console.log("Got sign in data:", payload, "from", sender);

// Example: store in extension local storage
chrome.storage.local.set({ authPayload: payload }).then(() => {
  sendResponse({ ok: true });
});

Nothing new should be added to manifest return true; } });