Build a Flask App with Okta for Secure OIDC Login and Authorized API Calls

Summary

Flask web applications require dedicated mechanisms to authenticate users securely and authorize access to downstream services. Developers can address this by integrating Okta as an OpenID Connect identity provider using the Authlib library. Authlib registers Okta as a remote provider and automates the Authorization Code flow using Proof Key for Code Exchange with SHA-256 code challenge verification. After logging in through Okta and completing the callback route, the Flask web application uses the acquired OAuth 2.0 access token to query a protected backend resource server. This architecture ensures that user credentials remain managed by Okta while client requests to backend API endpoints carry valid, scoped authorization tokens.

Context

Building Flask applications requires implementing secure user authentication and authorization mechanisms so that backend services only respond to verified, authorized client requests.

Approach / What changed

Configure an Okta OIDC web app integration, implement user authentication in Flask using Authlib with PKCE (S256), and forward the received OAuth access token to a protected resource server API.

Takeaways

• Authlib simplifies implementing the OIDC Authorization Code flow with PKCE in Flask by handling remote provider registration and S256 code challenge methods.
• Setting up Okta web application integrations requires configuring specific sign-in and sign-out redirect URIs, client credentials, and OIDC discovery metadata URLs.
• The client application uses the OAuth 2.0 access token acquired during user login to make authenticated requests to separate backend resource server endpoints.

Related reading

• Okta · Aug 21, 2026

  Add Cross App Access to Your OIDC Requesting Application

  OpenID Connect federated applications connecting to third-party services can implement Cross App Access using the Identity Assertion Authorization Grant specification. When a user authenticates via the standard authorization code flow, the requesting application retains the issued refresh token. The application exchanges this refresh token at Okta's token endpoint via RFC 8693 token exchange to receive a short-lived Identity Assertion Authorization Grant JSON Web Token. Next, the application presents this assertion to the third-party resource authorization server using the RFC 7523 JWT bearer grant to obtain a final access token. Developers can configure an AI Agent and application integrations in Okta to validate the entire end-to-end request flow against test endpoints on xaa.dev.

  Sohail Pathan

• Okta · Aug 24, 2026

  Add Cross App Access to Your OIDC Resource Application