> ## Documentation Index
> Fetch the complete documentation index at: https://developers.pleo.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Implementing the OAuth 2.0 Client Using a Library

export const WarningCallout = ({title, children}) => <div className="callout-box callout-warning">
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      </span>
      <div>
        {title && <div className="callout-title">
            {title}
          </div>}
        <div className="callout-body">
          {children}
        </div>
      </div>
    </div>
  </div>;

export const NoteCallout = ({title, children}) => <div className="callout-box callout-note">
    <div className="callout-row">
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      </span>
      <div>
        {title && <div className="callout-title">
            {title}
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          {children}
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<WarningCallout title="This page has now been ARCHIVED. Please visit:">
  * **[OAuth 2.0 Setup Workflow Guide](/docs/current/guides/oauth-workflow-guide)**
</WarningCallout>

Many open source libraries offer high-quality implementations of OAuth 2.0 clients. They are available in a variety of programming languages, offering support for various web frameworks and database backends.

<NoteCallout title="Note">
  Where to start. A list of open-source OAuth 2.0 client libraries is available at [https://oauth.net/code/](https://oauth.net/code/).
</NoteCallout>

We strongly recommend using one of these libraries instead of implementing OAuth 2.0 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

## Implementing OAuth 2.0 Client Using a Library

Libraries providing OAuth 2.0 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.

<NoteCallout title="Note">
  Details and capabilities of OAuth 2.0 implementations depend of the library
  your are selecting. Consult the documentation of the specific library you
  have selected.
</NoteCallout>

## Related Topics

* [OAuth 2.0 Implementation Reference Documentation](/docs/oauth-implementation-reference-documentation): Refer to this document to understand how the OAuth 2.0 authentication method is implemented.