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Many open source libraries offer high-quality implementations of OAuth clients. They are available in a variety of programming languages, offering support for various web frameworks and database backends.
Where to startA list of open-source OAuth client libraries is available at https://oauth.net/code/.
We strongly recommend using one of these libraries instead of implementing OAuth from scratch. Examples are:
  • Java: spring-security-oauth2-client, Apache OLTu
  • Python: authlib, Requests-OAuthlib
  • JavaScript: passport.js, oidc-client-js
  • .NET: Microsoft.Identity.Web

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Implementing OAuth Client Using a Library

Libraries providing OAuth implementation often allow customisation to some extent - allow to plug in custom implementations for front-end and back-end interfaces they provide. Most often, when using a library, a developer can: Benefits of using a library:
  • Configure the client with specific authorisation server: provide the authorisation and token endpoints, configure supported client authentication methods, and protocol extensions.
  • Provide the User Interface (UI) for initiating the authentication flow (connect to Pleo button), and connect it to functions and methods of the library that generate all necessary authentication request parameters.
  • Integrate the library with the web framework of choice to allow it to perform HTTP redirects.
  • Provide implementation for persistence backend, allowing the client library to store and retrieve parameters, such as code_verifier and state. Also, generate access and refresh tokens.
  • Provide custom UI for handling success and error responses from the authorisation server.
  • Listen to events emitted during flow and extend various stages.
Note: Details and capabilities of OAuth implementations depend of the library your are selecting. Consult the documentation of the specific library you have selected.