OAuth What Is It

OAuth is an authorization protocol used to allow an application to access resources from another service without sharing a password. It is behind common functions such as "sign in with Google" or "sign in with Facebook". In digital products, OAuth improves experience, increases conversion and reduces security risks. This guide explains what OAuth is, how it works, what flows exist, when to use it and what mistakes to avoid.

The objective is to provide a clear explanation for technical and product teams, with a focus on secure and business-aligned implementation.

What is OAuth

OAuth (Open Authorization) is an open standard that allows you to delegate access. Instead of the user providing their password to a third-party app, they authorize access directly from the provider (Google, Apple, GitHub). The app receives a token with limited permissions.

This protects data, improves UX, and gives you control over what the app can access.

Difference between authentication and authorization

Many people confuse:

Authentication: check who the user is.
Authorization: define what he can access.

OAuth is an authorization protocol. For authentication, you typically use OpenID Connect, which works on top of OAuth.

How the OAuth flow works

In simplified form:

The user clicks on "sign in with".
The app redirects to the provider.
The user authorizes.
The provider returns a token.
The app uses the token to access permitted resources.

This process prevents password sharing.

Main OAuth flows

Authorization Code

Safer. Used in web and mobile apps with backend.

Implicit

Older, less secure. Today in disuse.

Client Credentials

Used for communication between servers.

Device Code

Used on devices without a full browser.

The choice depends on the type of application.

Tokens and scopes

OAuth uses access tokens. Each token has scopes, which define permissions. Example: access to email, profile or contact list. The app should only ask for what is necessary, to avoid user rejection.

Tokens can expire and be renewed by refresh tokens, ensuring security without requiring constant login.

OAuth and social login

Social login increases conversion because it reduces friction. Instead of creating a password, the user uses a trusted provider. This improves UX and reduces forgotten passwords.

On the other hand, the app is dependent on the provider. Therefore, it is recommended to have a traditional login option as an alternative.

Risks and vulnerabilities

If poorly implemented, OAuth can generate risks:

Malicious redirects.
Leaked tokens.
Excessive scopes.
Lack of state validation.

Good practices reduce these risks.

Good security practices

Use Authorization Code with PKCE in mobile apps.
Always validate state to avoid CSRF.
Use HTTPS at all stages.
Store tokens securely.
Order only necessary scopes.

OAuth in mobile apps

In mobile apps, the recommendation is to use PKCE, which protects against code interception. Login must open the system browser for greater security.

OAuth in APIs

APIs use OAuth to control access. This allows for tokens with limited scopes and quick revocation. A well-protected API improves reliability and scalability.

When to use OAuth

Use OAuth when:

You want social login.
Need to access data from other services.
Want to delegate secure access.

Do not use OAuth if the system is completely internal and controlled.

Quick checklist

Choose correct flow.
Implement PKCE.
Define minimum scopes.
Validate state.
Use HTTPS.
Monitor tokens.

Conclusion

OAuth is an essential standard for social login and secure access to third-party data. When implemented well, it improves the user experience and increases security. The key is to choose the right flow, limit scopes and protect tokens. This ensures trust and reduces risks in the long term.

##FAQs

1) OAuth and login?
No. He is authorization. For login, use OpenID Connect.

2) Is OAuth secure?
Yes, if implemented correctly.

3) Do I need OAuth in my app?
Only if you use social login or access third-party data.

4) Is PKCE mandatory?
Yes, in mobile apps and highly recommended in web apps.

5) Does OAuth replace password?
No. It can reduce password usage, but does not eliminate it completely.