When you sign out the currently signed-in user with:
gapi.auth2.getAuthInstance().signOut();
And then call:
gapi.auth2.getAuthInstance().signIn();
The previously signed-in user will automatically get signed in again.
How do I instead show the option to sign in with a different Google account? Does signOut() not actually sign out the user?
You can force showing the account selection screen by passing the prompt SignInOptions option to signIn():
gapi.auth2.getAuthInstance().signIn({
prompt: 'select_account'
});
signOut() signs the user out of your app without signing them out of Google. Therefore, the same user can sign back into your app without a prompt, because they are already signed into Google and because the app still has access to all the previously-accepted scopes.
You could remove the previously-accepted scopes by calling disconnect(), but then the user will have to accept the same scopes again, which is probably not what you want.