What are OAuth 2.0 credentials?
OAuth 2.0 is the most widely adopted authorization standard in modern APIs. OAuth credentials include four token types: Client ID (public identifier of your application), Client Secret (private key you never expose to clients), Access Token (temporary token with specific permissions, typically JWT) and Refresh Token (long-lived token to renew expired access tokens).
Each credential serves a specific role: the Client ID identifies your app to the OAuth server, the Client Secret authenticates that it's really you (never include it in frontend code), the Access Token authorizes each request (sent in Authorization: Bearer header) and the Refresh Token lets you obtain new access tokens without asking the user to log in again. Access tokens typically last minutes or hours; refresh tokens can last days or months.
This generator produces credentials with realistic format: Client IDs of 32-64 alphanumeric characters or UUIDs, Client Secrets with prefixes like sk_live_ or cs_prod_, Access Tokens in JWT format (three parts separated by dots) or long random strings, and Refresh Tokens of 64-128 characters. Useful for mocking responses, documenting APIs, creating test fixtures or designing interfaces.
Common mistakes when implementing OAuth
The number one error is exposing the Client Secret in the frontend. The secret must live only in your backend; if you include it in browser JavaScript, anyone can read it and impersonate your app. Use the PKCE (Proof Key for Code Exchange) flow for public apps like SPAs or mobile.
Another frequent problem: not validating the token scope. An access token with read:user scope shouldn't be able to write data. Always verify that token permissions match the operation. It's also critical to not assume the token is eternal: implement logic to detect expired tokens (status 401) and renew them automatically with the refresh token.
Many devs forget to rotate refresh tokens. When you generate a new access token, also issue a new refresh token and revoke the previous one (rotation pattern). This limits damage if a refresh token leaks. And never store tokens in localStorage without encryption: prefer HttpOnly cookies or native secure storage on mobile.
Finally, don't log complete tokens. If you need to debug, log only the last 6 characters (token ending in ...a1b2c3). A token in a log can compromise your entire security if those logs are accessible or leak.
Differences between OAuth 2.0 flows
OAuth 2.0 defines several flows depending on your application type. Authorization Code is the most secure for apps with backend: the user authorizes, you receive a temporary code, exchange it for tokens on the server (where you keep the secret). This flow prevents tokens from appearing in browser URLs.
Authorization Code + PKCE extends the previous flow for public apps (SPAs, mobile): you generate a random code_verifier, send its hash (code_challenge) when requesting authorization and then prove you knew the original verifier. This makes the Client Secret unnecessary, ideal when you don't have a backend or can't protect secrets.
Client Credentials is for server-to-server communication (machine-to-machine): your backend authenticates directly with Client ID + Secret, without user intervention. Useful for jobs, microservices or backend integrations. Tokens typically have scope limited to the app's own resources.
Implicit (deprecated) delivered tokens directly in the redirect URL, without intermediate code. It was convenient but insecure: tokens exposed in browser history. Replace it with Authorization Code + PKCE. Resource Owner Password (also deprecated) involved sending username/password to your app; only valid in legacy scenarios where you control both ends.
OAuth security best practices
Always use HTTPS in production: OAuth without TLS is like sending passwords in plain text. Validate the exact redirect_uri (no wildcards) to prevent open redirect attacks. Keep a whitelist of allowed URIs and reject any variation.
Implement state parameter to prevent CSRF: generate a random token before redirecting to the OAuth server, save it in session and verify it matches when returning. If it differs, abort the flow. Some providers also support nonce to prevent replay attacks on JWT tokens.
Rotate secrets periodically (every 90-180 days) and revoke tokens when the user logs out or changes password. Many OAuth APIs offer revocation endpoints; using them invalidates tokens immediately. Don't rely only on expiration: a stolen refresh token can keep working for months.
Limit scope to the minimum necessary: if you only read profile, don't request write. This reduces the impact of a breach. And monitor anomalous usage: many access tokens from different IPs in minutes can indicate leakage. Implement rate limiting per token to mitigate abuse.