What you agree to when you tap Sign in with Google

You are three taps into a new app and it wants an account. At the top are two buttons with a familiar logo, and underneath them a form asking you to invent a password you will never remember. The buttons are faster. The question is what they cost.

Google answers that on its own help page. When you use Sign in with Google, "Google only shares the following information associated with your Google Account: Your name / Your email address / Your profile picture." Three things. The same page adds one more sentence. "Google doesn't share your Google Account password with the linked app."

That's the whole mechanism. Google vouches for you. The app gets a yes, plus three fields, and no password of yours to store, lose, or leak.

What each button hands over

Google. Name, email address, profile picture. An app can ask for more, your Gmail or your Drive or your Calendar, and Google puts that on a separate screen. "Before Google shares any of your data with an app from a developer other than Google, you'll find a list of the data and services that the app wants to access." That screen is the one people click through without reading. Read it. A note-taking app that wants your basic profile is ordinary. A note-taking app that wants to read your email is answering a different question.

Apple. Name and email, and Apple's page is specific about the first sign-in. "At your first sign in, apps and websites can ask only for your name and email address to set up an account for you." You also get a choice the other buttons do not offer. Tap Hide My Email and Apple creates "a unique, random email address that forwards to your personal email." The app gets something ending in privaterelay.appleid.com. Your real address stays with Apple. You can reply straight through the relay address and the app still never sees the real one.

Facebook. Meta's developer documentation is where the plain wording lives. The "public_profile" permission "allows an app to read the Default Public Profile Fields on the User node," and it "is automatically granted to all apps," which means no separate review. The app asks separately for the "email" permission to "read a person's primary email address." Meta's consumer help pages would not open for verification, so I am quoting the developer docs rather than a page written for you. If you're choosing between the three buttons, Facebook is the one I'd leave alone, because it's the one whose disclosures I couldn't read.

Apple requires two-factor for Sign in with Apple. Google does not require it for Sign in with Google, which is the reason the next section is about turning it on. Google's own description of why it exists is to "add an extra layer of security to your account in case your password is stolen." With it on, whoever wants into that app through the button has to get past your sign-in first, which means getting past the code or the prompt or the face.

The one-basket question

Everyone arrives at the same objection. All my apps behind one account, and if that account goes, everything goes.

The basket already exists. Every app you sign up for with an email and a password sends its password resets to that email address. Whoever holds your email holds every account you have, button or no button. The mailbox has been the master key the entire time.

What the button changes is the weak link. A password you invent for a small app is a password that app now stores. If it leaks, and you used something close to it elsewhere, the leak travels. Google's instruction on the subject is blunt about the alternative. "Do not share your Google Account password on a third-party app."

So the work moves to the one account, where it belongs. Two-step verification on. A recovery phone and a recovery email set, which is also where the recovery check comes in. Google buries one timing catch in its recovery page, and it's the reason to do this today rather than the day you need it. "If you change your account recovery info, it may take up to 7 days for those changes to take effect."

Your bank and your email still get their own unique password out of a password manager. The button is for the recipe site, the parking app, the store you buy from twice a year.

Disconnecting is not deleting

Disconnecting and deleting are two different jobs. Both companies put the difference in writing, in wording specific enough to quote.

Take the Google link away and Google "stops automatic sign-in to the app. This doesn't delete your data on the app." The account you created is still there with whatever you gave it. Google goes further. "When you remove access, the app may keep info you provided when you signed in with your Google Account. You may need to ask them to delete the data they already have."

Apple describes the same shape. Stop using your Apple Account with an app and "you're signed out of the app on your device." Sign in with Apple again later and "you're signed in to the same account that you previously used." Closing the door leaves the room furnished, so the second job has to happen inside the app.

Deleting the app off your phone does less than that. It removes the app. The link and the account both survive it.

The page that lists all of them

Both companies keep one screen with every app you have ever signed into this way, and most people have never opened theirs.

Google. Go to your Google Account's linked apps page, at myaccount.google.com/linkedapps. Select Sign in with Google, pick an app, choose See details, then 'Stop using Sign in with Google', then Confirm. The same page has two other tabs that do different jobs. 'Linked account' covers apps that have given Google access to your account with them, and 'Access to your Google Account' covers apps you let reach data inside your Google Account, such as contacts, photos, playlists, Gmail, or Drive. If you are cleaning house, walk all three.

Apple. On an iPhone or iPad, Settings, then your name, then Sign in with Apple. On a Mac, the Apple menu, then System Settings, then your name, then Sign in with Apple. From any browser on any device, including a Pixel or a Windows PC, sign in at account.apple.com and go to Sign-In & Security, then Sign in with Apple. Pick an app and you can stop using the button for it, or leave the sign-in alone and turn off 'Forward To' so the relay address stops delivering mail.

One catch on the relay. Turning forwarding off for an app needs no subscription. Changing which inbox a relay address forwards to requires an iCloud+ subscription, and so does creating relay addresses for sites that have no Apple button.

Open your list

Go to myaccount.google.com/linkedapps and read your own list. Mine had apps on it I couldn't place, from services I used once years ago. Cut the ones you don't recognize. Then finish the job inside the two or three that matter to you, by deleting the account there.

After that, the next time a new app offers you the button, you know what it takes and where the undo lives.

Which did you find on your list that you had forgotten about? I collect these, and I suspect half of us have a travel app from a trip we took in 2019. joel@freshfromcache.com