missing emails in firebase auth for 20% of facebook credentials - firebase

Question

I allow users to login with facebook on my app, backed by firebase authentication.
In around 20% of the facebook logins, I don't receive the user's email. I need the email address in my app, and can't figure out why I don't receive it.
Since I get the email address 80% of the time, I assume I have the right permissions setup to retrieve it.
I also enforced "One account per email address" in firebase-auth, so it seems to be a different issue than that raised in Firebase Auth missing email address.
Relevant extracts of my code:
export const FacebookSignUp: React.FC<SocialAuthProps & { title?: string }> = ({ onError, onSetWaiting, title }) => {
async function onFacebookButtonPress() {
onSetWaiting(true);
const { email, first_name, accessToken } = await getFacebookUserData();
const couldLogin = await tryLoginWithFacebook(email, accessToken);
if (!couldLogin) {
// Create a Firebase credential with the AccessToken
const facebookCredential = FacebookAuthProvider.credential(accessToken);
const userCredential = await firebaseAuth.signInWithCredential(facebookCredential);
if (userCredential.user === null) {
throw new Error("Null user");
}
const signupUser: SignupUserData = {
userId: userCredential.user.uid,
email,
pseudo: first_name || undefined
};
await createSignupUser(signupUser).then(() => {
onSetWaiting(false);
});
}
}
return (
<SocialButton
iconName="facebookIcon"
title={title || "S'inscrire avec Facebook"}
onPress={() =>
onFacebookButtonPress().catch((err) => {
onSetWaiting(false);
if (err instanceof SocialAuthError) {
onError(err);
} else if (err instanceof Error) {
const { message, name, stack } = err;
serverError("Unexpected signup error", { message, name, stack });
}
})
}
/>
);
};
import { LoginManager, AccessToken, GraphRequest, GraphRequestManager } from "react-native-fbsdk";
export async function getFacebookUserData(): Promise<FacebookInfo> {
LoginManager.logOut();
const result = await LoginManager.logInWithPermissions(["public_profile", "email"]);
if (result.isCancelled) {
throw "User cancelled the login process";
}
// Once signed in, get the users AccesToken
const { accessToken } = (await AccessToken.getCurrentAccessToken()) || {};
if (!accessToken) {
throw "Something went wrong obtaining access token";
}
return new Promise((resolve, reject) => {
let req = new GraphRequest(
"/me",
{
httpMethod: "GET",
version: "v2.5",
parameters: {
fields: {
string: "email,first_name"
}
}
},
(err, res) => {
if (err || res === undefined) {
reject(err);
} else {
const { first_name, email } = res as { first_name: string; email: string };
resolve({ first_name, email, accessToken });
}
}
);
new GraphRequestManager().addRequest(req).start();
});
}

Answer 1

Facebook allows you to opt out of passing your email along to third-party apps. You can request it, but the user can deny it.
If I ever log in with Facebook I always opt out of passing my email along - most of the time, the third-party app doesn't need it for legitimate purposes.
"I need the email address in my app" - why? email marketing? account duplication prevention?
In cases where you did not get an email, assume the user has opted-out and/or doesn't have an email tied to their account. If you need one, ask the user to input a contact email address and explain what you are using it for. Expect some users to still opt out and plan around it.
You could always convert their username into a non-existent email like theirusername#noreply.users.yourapp.com depending on your use case.