Facebook sign-in in Firebase - Step-by-Step Execution

Process Flow - Facebook sign-in

User clicks Facebook Sign-In button

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App calls Firebase Facebook Auth

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Firebase opens Facebook login popup

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User enters Facebook credentials

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Facebook verifies credentials

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Facebook returns access token to Firebase

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Firebase verifies token and signs in user

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App receives user info and updates UI

The user clicks the Facebook sign-in button, triggering Firebase to open a Facebook login popup. After the user logs in, Facebook sends a token to Firebase, which verifies it and signs in the user.

Execution Sample

Firebase

const provider = new firebase.auth.FacebookAuthProvider();
firebase.auth().signInWithPopup(provider)
  .then((result) => {
    const user = result.user;
    console.log('User signed in:', user.displayName);
  })
  .catch((error) => console.error(error));

This code triggers a Facebook login popup via Firebase and logs the signed-in user's name on success.

Process Table

Step	Action	Firebase State	Facebook State	Result
1	User clicks Facebook sign-in button	Idle	Idle	Popup triggered
2	Firebase opens Facebook login popup	Waiting for Facebook login	Waiting for user input	Popup visible
3	User enters Facebook credentials	Waiting for Facebook response	Verifying credentials	Credentials submitted
4	Facebook verifies credentials	Waiting for token	Verified credentials	Access token generated
5	Facebook returns access token to Firebase	Verifying token	Token sent	Token received
6	Firebase verifies token and signs in user	Signed in	Idle	User authenticated
7	App receives user info and updates UI	Signed in	Idle	User info displayed
8	Process complete	Signed in	Idle	Ready for next action

💡 User successfully signed in after Firebase verified Facebook token

Status Tracker

Variable	Start	After Step 3	After Step 5	Final
provider	undefined	FacebookAuthProvider instance	FacebookAuthProvider instance	FacebookAuthProvider instance
result	undefined	undefined	Auth result with token	Auth result with user info
user	undefined	undefined	undefined	User object with displayName

Key Moments - 3 Insights

Why does the app open a popup instead of redirecting immediately?

The popup allows the app to keep control and handle the login without leaving the page, as shown in execution_table step 2.

What happens if the user enters wrong Facebook credentials?

Firebase will catch an error in the catch block (not shown in table), preventing sign-in and showing an error message.

Why do we need to verify the Facebook token in Firebase?

Firebase verifies the token to ensure it is valid and issued by Facebook, securing the sign-in process as in execution_table step 6.

Visual Quiz - 3 Questions

Look at the execution table, at which step does Firebase receive the Facebook access token?

A Step 5

B Step 3

C Step 6

D Step 7

💡 Hint

Check the 'Result' column for when the token is received by Firebase.

According to the variable tracker, when is the 'user' variable first assigned a value?

A After Step 3

B After Step 5

C Final

D Start

💡 Hint

Look at the 'user' row and see when it changes from undefined.

If the user cancels the Facebook login popup, what would happen in the execution flow?

A Firebase signs in the user anyway

B Firebase catches an error and sign-in fails

C The popup stays open indefinitely

D User info is displayed without login

💡 Hint

Consider what happens when credentials are not provided or login is aborted.

Concept Snapshot

Facebook sign-in with Firebase:
- Create FacebookAuthProvider instance
- Call signInWithPopup(provider)
- User logs in via popup
- Facebook returns access token
- Firebase verifies token and signs in user
- App receives user info and updates UI
- Errors handled in catch block

Full Transcript

This visual execution traces the Facebook sign-in process using Firebase. The user clicks the sign-in button, triggering Firebase to open a Facebook login popup. The user enters credentials, which Facebook verifies and returns as an access token. Firebase then verifies this token and signs in the user. The app receives the user information and updates the interface accordingly. Variables like 'provider', 'result', and 'user' change state through the process. Key moments include understanding why a popup is used, error handling for wrong credentials, and token verification for security. The quizzes test understanding of token receipt, variable assignment, and error scenarios.