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Flow Cache Design Doc

Overview

This design doc outlines the proposed solution for caching the flow object in the OAuth2 exchange between the Client, Ory Hydra, and the Consent and Login UIs. The flow object contains the state of the authorization request.

Problem Statement

Currently, the flow object is stored in the database on the Ory Hydra server. This approach has several drawbacks:

Each step of the OAuth2 flow (initialization, consent, login, etc.) requires a database query to retrieve the flow object, and another to update it.
Each part of the exchanges supplies different values (login challenge, consent challenge, etc.) to identify the flow object. This means the database table has multiple indices that slow down insertions.

Proposed Solution

The proposed solution is to store the flow object in client cookies and URLs. This way, the flow object is written only once when the flow is completed and the final authorization code is generated.

Requirements

The flow object must be stored in client cookies and URLs.
The flow object must be secure and protect against unauthorized access.
The flow object must be persistent, so that the flow can be resumed if the user navigates away from the page or closes the browser.
The flow object must be scalable and able to handle a large number of concurrent requests.

Architecture

The proposed architecture for the flow cache is as follows:

Store the flow object in an AEAD encrypted cookie.
Pass a partial flow around in the URL.
Use a secure connection to protect against unauthorized access.

sequenceDiagram
    actor Client
    participant Hydra
    participant LoginUI as Login UI
    participant ConsentUI as Consent UI
    % participant Callback

    autonumber

    Client->>+Hydra: GET /oauth2/auth?client_id=CLIENT_ID&response_type=code&scope=SCOPES&state=STATE
    Hydra->>-Client: Redirect to <br> http://login.local/?login_challenge=LOGIN_CHALLENGE

    Client->>+LoginUI: GET /?login_challenge=LOGIN_CHALLENGE
    LoginUI->>Hydra: GET /admin/oauth2/auth/requests/login
    Hydra->>LoginUI: oAuth2LoginRequest
    alt accept login
      LoginUI->>Hydra: PUT /admin/oauth2/auth/requests/login/accept
    else reject login
      LoginUI->>Hydra: PUT /admin/oauth2/auth/requests/login/reject
    end
    Hydra->>LoginUI: oAuth2RedirectTo
    LoginUI->>-Client: Redirect to <br> http://hydra.local/oauth2/auth?client_id=CLIENT_ID&login_verifier=LOGIN_VERIFIER&response_type=code&scope=SCOPES&state=STATE

    Client->>+Hydra: GET /oauth2/auth?client_id=CLIENT_ID&login_verifier=LOGIN_VERIFIER&response_type=code&scope=SCOPES&state=STATE
    Hydra->>-Client: Redirect to <br> http://consent.local/?consent_challenge=CONSENT_CHALLENGE

    Client->>+ConsentUI: GET /?consent_challenge=CONSENT_CHALLENGE
    ConsentUI->>Hydra: GET /admin/oauth2/auth/requests/consent
    Hydra->>ConsentUI: oAuth2ConsentRequest
    alt accept login
      ConsentUI->>Hydra: PUT /admin/oauth2/auth/requests/consent/accept
    else reject login
      ConsentUI->>Hydra: PUT /admin/oauth2/auth/requests/consent/reject
    end
    Hydra->>ConsentUI: oAuth2RedirectTo
    ConsentUI->>-Client: Redirect to <br> http://hydra.local/oauth2/auth?client_id=CLIENT_ID&consent_verifier=CONSENT_VERIFIER&response_type=code&scope=SCOPES&state=STATE

    Client->>+Hydra: GET /oauth2/auth?client_id=CLIENT_ID&consent_verifier=CONSENT_VERIFIER&response_type=code&scope=SCOPES&state=STATE
    Hydra->>-Client: Redirect to <br> http://callback.local/callback?code=AUTH_CODE&scope=SCOPES&state=STATE
    Note over Hydra,Client: next, exchange code for token.


    % Client->>+Callback: GET /callback?code=AUTH_CODE&scope=SCOPES&state=STATE
    % Callback->>-Client: Return Authorization Code

Step 2:

Set the whole flow as an AEAD encrypted cookie on the client
The cookie is keyed by the state, so that multiple flows can run in parallel from one cookie jar
Set the LOGIN_CHALLENGE to the AEAD-encrypted flow

Step 5:

Decrypt the flow from the LOGIN_CHALLENGE, return the oAuth2LoginRequest

Step 8:

Encode the flow into the redirect URL in oAuth2RedirectTo as the LOGIN_VERIFIER

Step 11

Check that the login challenge in the LOGIN_VERIFIER matches the challenge in the flow cookie.
Update the flow based on the request from the LOGIN_VERIFIER
Update the cookie
Set the CONSENT_CHALLENGE to the AEAD-encrypted flow

Step 14:

Decrypt the flow from the CONSENT_CHALLENGE

Step 17:

Encode the flow into the redirect URL in oAuth2RedirectTo as the CONSENT_VERIFIER

Step 20

Check that the consent challenge in the CONSENT_VERIFIER matches the challenge in the flow cookie.
Update the flow based on the request from the CONSENT_VERIFIER
Update the cookie
Write the flow to the database
Continue the flow as currently implemented (generate the authentication code, return the code, etc.)

Client HTTP requests

For reference, these HTTP requests are issued by the client:

GET http://hydra.local/oauth2/auth?client_id=CLIENT_ID&nonce=NONCE&response_type=code&scope=SCOPES&state=STATE
Redirect to http://login.local/?login_challenge=LOGIN_CHALLENGE
GET http://login.local/?login_challenge=LOGIN_CHALLENGE
Redirect to http://hydra.local/oauth2/auth?client_id=CLIENT_ID&login_verifier=LOGIN_VERIFIER&nonce=NONCE&response_type=code&scope=SCOPES&state=STATE
GET http://hydra.local/oauth2/auth?client_id=CLIENT_ID&login_verifier=LOGIN_VERIFIER&nonce=NONCE&response_type=code&scope=SCOPES&state=STATE
Redirect to http://consent.local/?consent_challenge=CONSENT_CHALLENGE
GET http://consent.local/?consent_challenge=CONSENT_CHALLENGE
Redirect to http://hydra.local/oauth2/auth?client_id=CLIENT_ID&consent_verifier=CONSENT_VERIFIER&nonce=NONCE&response_type=code&scope=SCOPES&state=STATE
GET http://hydra.local/oauth2/auth?client_id=CLIENT_ID&consent_verifier=CONSENT_VERIFIER&nonce=NONCE&response_type=code&scope=SCOPES&state=STATE
Redirect to http://callback.local/callback?code=AUTH_CODE&scope=SCOPES&state=STATE
GET http://callback.local/callback?code=AUTH_CODE&scope=SCOPES&state=STATE

Implementation

The implementation of the flow cache will involve the following steps:

Modify the Ory Hydra server to store the flow object in an AEAD encrypted cookie.
Modify the Consent and Login UIs to include the flow object in the URL.
Use HTTPS to protect against unauthorized access.

Conclusion

The proposed solution for caching the flow object in the OAuth2 exchange between the Client, Ory Hydra, and the Consent and Login UIs is to store the flow object in client cookies and URLs. This approach eliminates the need for a distributed cache and provides a scalable and secure solution. The flow object will be stored in an AEAD encrypted cookie and passed around in the URL. HTTPS will be used to protect against unauthorized access.

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