> For the complete documentation index, see [llms.txt](https://docs.thunkable.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.thunkable.com/blocks/app-features/sign-in.md).

# Sign In Blocks

## Overview

Authentication is the process by which your app’s users sign up or sign in to your app. It confirms the legitimacy of a user's identity before allowing them to interact with the application. 

Thunkable supports authentication through:

{% content-ref url="/pages/WIkJxydctAv4Z0IHKTHK" %}
[User Sign Up, Sign In, and Authentication with Firebase](/blocks/app-features/sign-in/sign-in.md)
{% endcontent-ref %}

{% content-ref url="/pages/afVi7mBt7fMkwXE5wLyw" %}
[User Sign Up, Sign In, and Authentication with Google](/blocks/app-features/sign-in/sign-in-1.md)
{% endcontent-ref %}

{% content-ref url="/pages/QQpFDowIjy05ldVe7kSx" %}
[User Sign Up, Sign In, and Authentication with Apple](/blocks/app-features/sign-in/user-sign-up-sign-in-and-authentication-with-apple.md)
{% endcontent-ref %}