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Aries Cloudagent Web Application Integration Guidelines

This document outlines best practices and guidelines to be considered and implemented when integrating an existing system with Aries Cloudagent.

Architecture

Generally speaking, a web application that leverages Aries agents is structured as follows:

  • Agent: this service is used by the web application to interact with a Ledger and other agents connected to the same ledger. It is generally not controlled directly by the web application frontend, instead requests to the agent come from a controller service.
  • Controller: this service provides the business logic for the web application, and acts as bridge between the frontend and the agent. The controller usually exposes appropriate APIs that the frontend will use to perform common business tasks as well as agent-related tasks such as requesting the creation of a new connection, etc. The controller is also tasked with tracking and managing all of the information that is required for the business processes to be implemented and work successfully.
  • Frontend: this service is what the users see and interact with, commonly something that is displayed in a web browser.

The above components may be at times partially consolidated or further split into separate services, the purpose of this overview is to explain the separation of concerns of these three macro-areas.

Creating and Managing Connections

A connection is a communication channel established between two Aries agents. It allows them to send and receive data and interact: issuing a credential or requesting/sending a proof request require, in most cases, a valid, active connection to be completed.

The closest relative of a connection between Aries agents in the web application world is a session: for this reason the recommended way of tracking open connections in a web application is to use a session cookie.

Implementation

As discussed previously, to establish a new connection the frontend would call the appripriate controller API endpoint to create a new connection invitation. The controller would translate this request to the appropriate call to the admin APIs in the agent service, and return the data that will be displayed in a QR code for the mobile wallet to scan and use.

A connection is identified within an agent by an id. This id is used when retrieving connection information as well as when instructing the agent to send/request something via a specific channel.

When creating/requesting new connections, the web application should set and manage a session cookie whose payload corresponds to the UUID of the connection being targeted/used.

Important: the session cookies shuld be set to Secure and HttpOnly to mitigate the risk of exposing its contents to the web, as well as the risk of cross-site scripting attacks.
Connections do not expire, however they can be deleted by either agent involved in the protocol: the cookie should therefore not expire, or have an expiration date that is longer than the average lapse of time between interactions between the user and the service.

  1. First interaction: the applications's frontend sends a request for a new connection to the controller. No cookie is being passed in the headers since no connection was yet established, therefore the controller proceeds to generate a new connection invitation with its agent, and sends a response to the frontend using the Set-Cookie header to create a new cookie with the connection's UUID as payload.
  2. Second interaction: following the first interaction, both agents will have established a connection that can be reused for future protocol exchanges. When initiating a new agent interaction from the frontend's UI, the client will send a request for a new connection to the controller, including the previously created cookie in the header. The controller will use that information to initiate the appropriate task on the specified channel. The frontend will not display a QR code to establish a new connection and will send a response setting the cookie, again, with the same value..
    • i.if the controller has lost/removed the connection record specified in the cookie, it will proceed to generate a new connection invitation in a similar way to the first interaction. It will then send the response to the frontend, that will display a new QR code for the user to scan. The response will include a new Set-Cookie header, populated with the new connection UUID.
    • if the session cookie was removed from the frontend, the connection request would not include a value for the cookie and would therefore be considereed by default as a new connection request.
    • if the user has removed the connection from their wallet, the UI should display controls to establish a new connection. The controller will likely attempt to communicate on the existing connection, while the frontend should display a "get a new connection" control after a few seconds to allow users to recover from this state.

Note: while it shoudn't be a problem to keep old "dead" connection records in the agent, it seems like good practice for the controller to instruct the agent to remove connections being replaced. The controller should be tracking the appropriate information to facilitate this process and no recommendation will therefore be made on how to implement/achieve this.

Interaction Diagram

First Interaction

Describes flow for first interaction (no previously established connection) and/or browser cookies cleared/absent. It lso applies to the - less likely - scenario where the connection was deleted on the controller/agent side.

Created with Raphaël 2.2.0Mobile WalletMobile WalletFrontendFrontendControllerControllerAgentAgentRequest Connection/connections/create-invitationNew Invitation ID: 12345New Invitation (Set-Cookie: 12345)Create QR codeScan QR CodeEstablish ConnectionWebhook: connection 12345 establishedDo something (request proof, issue credential, etc.)Using connection

Following Interactions

Describes flows for 2nd and following interactions, when a session cookie is available and the connection is present and active on both mobile wallet and agent.

Created with Raphaël 2.2.0Mobile WalletMobile WalletFrontendFrontendControllerControllerAgentAgentRequest Connection (Set-Cookie: 12345)Connection 12345 exists (may also check with agent)Do something (request proof, issue credential, etc.)Response (Set-Cookie: 12345)Using connectionDisplay connection recovery button after 2s-3sWebhook updates
Following Interactions - Recovery

Describes the flow for 2nd and following interaction, in the scenario where the connection was removed from the mobile wallet, and a session cookie is available

Created with Raphaël 2.2.0Mobile WalletMobile WalletFrontendFrontendControllerControllerAgentAgentRequest Connection (Set-Cookie: 12345)Connection 12345 exists (may also check with agent)Do something (request proof, issue credential, etc.)Response (Set-Cookie: 12345)Using connectionDisplay connection recovery button after 2s-3sWebhook updatesClick recovery buttonRequest Connection/connections/create-invitationNew Invitation ID: 56789New Invitation (Set-Cookie: 56789)Create QR codeScan QR CodeEstablish ConnectionWebhook: connection 56789 establishedDo something (request proof, issue credential, etc.)Using connection
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