OBOFunction

This repository contains the BFF proxy for a SharePoint-hosted SPFx web part that talks to a Microsoft Foundry hosted agent as the signed-in user.

Current architecture

SPFx web part (SharePoint page)
  -> POST /api/agent/chat
  -> OBOFunction proxy (App Service, .NET 8)
  -> OBO to https://ai.azure.com/.default
  -> HostedSecureMcpAgent (existing Foundry hosted agent, outside this repo)
  -> agent-owned Toolbox / MCP / downstream tools

What is in this repo

Component	Path	Purpose
BFF proxy	src/OBOFunction	Validates the SPFx JWT, extracts the user bearer token, performs OBO to Foundry, and forwards chat turns to the configured hosted agent.
SPFx sample	spfx-sample/spfx-profile-agent	Reference client that calls the proxy with AadHttpClient.
Infra	infra/	Bicep for the proxy App Service, App Insights, Log Analytics, plan, and user-assigned managed identity.
Tests	test/OBOFunction.Tests	Unit tests for the proxy’s Foundry response parsing and error handling.

What is not in this repo anymore

• No local hosted-agent project
• No local search_faq tool implementation
• No local profile-fetching service
• No Key Vault dependency in the runtime path
• No Azure Functions host / Functions-specific runtime model

The actual hosted agent is HostedSecureMcpAgent in Foundry and is configured through proxy app settings. The hosted-agent source is published at gbelenky/HostedSecureMcpAgent:

• Foundry__AgentName=HostedSecureMcpAgent
• Foundry__AgentResponsesUrl=https://rsc-fdr-swc.services.ai.azure.com/api/projects/prj-fdr-swc/agents/HostedSecureMcpAgent/endpoint/protocols/openai/responses?api-version=v1

Why the BFF proxy is required

The proxy is not incidental; it is the design boundary that makes this solution viable.

1. SPFx is a public client, but OBO needs a confidential client

The browser can obtain a user token for api://<proxy-app>, but it cannot safely hold the client secret required to perform the OBO exchange to the Foundry data plane. The proxy is the one confidential component allowed to hold that secret.

2. The browser must not call Foundry directly

The Foundry Responses endpoint is a server-side API. In this solution, the browser talks only to SharePoint and the proxy. Keeping Foundry behind the proxy:

• keeps the Foundry endpoint, auth scope, and agent routing out of the client bundle;
• avoids exposing server-side credentials or bearer-token minting logic in the browser; and
• gives the app one stable API contract: POST /api/agent/chat.

3. The proxy is the policy and trust boundary

The proxy enforces:

• JWT validation (aud, issuer, signature)
• SharePoint-origin CORS
• RFC 7807 error shaping
• conversation continuity handling (previousResponseId)
• server-side telemetry and trace correlation

Without the proxy, those controls would have to move into an environment that cannot safely own them: the browser.

4. The live system proves the proxy’s role

The live SharePoint page was validated end-to-end through this path:

• SharePoint page -> SPFx web part
• SPFx web part -> https://app-proxy-z6vb2tjg2j4ye.azurewebsites.net/api/agent/chat
• Proxy -> HostedSecureMcpAgent

That browser verification returned:

• a greeting for the signed-in user
• the signed-in user’s profile from the hosted agent path

So the proxy is not theoretical; it is the working production integration point.

For deeper reasoning, see ARCHITECTURE.md.

Runtime behavior

POST /api/agent/chat

Request:

{ "message": "What is my profile?" }

or for first-load greeting:

{ "message": "", "greeting": true }

Follow-up turn:

{ "message": "And what about vacation policy?", "previousResponseId": "caresp_..." }

Response:

{ "reply": "...", "responseId": "caresp_...", "status": "success" }

Health

• GET /liveness
• GET /readiness

Configuration

Proxy app settings

Setting	Purpose
AzureAd__TenantId	Entra tenant for inbound JWT validation and OBO
AzureAd__ClientId	Proxy app registration client id
AzureAd__Audience	Expected audience (api://<client-id>)
AzureAd__ClientSecret	Confidential secret used for OBO
SharePoint__TenantHostname	Allowed SharePoint origin for CORS
Foundry__ProjectEndpoint	Foundry project base endpoint
Foundry__AgentName	Hosted agent name (HostedSecureMcpAgent)
Foundry__AgentResponsesUrl	Explicit Responses endpoint override
Foundry__ApiVersion	Foundry Responses API version (v1)
Foundry__TokenScope	OBO target scope (https://ai.azure.com/.default)

App registration

One app registration is used for the proxy API:

• exposes access_as_user
• is requested by SPFx through AadHttpClient
• is the confidential client that performs OBO to Foundry

Deploy

This repo now deploys only the proxy.

cd C:\src\OBOFunction
azd up

Useful follow-up commands:

azd deploy api
azd env get-values

Local development

cd C:\src\OBOFunction\src\OBOFunction
dotnet run

Default local URL from launchSettings.json:

• http://localhost:7071

REST client sample:

• http/agent-chat.http

Validation

Build

dotnet build .\src\OBOFunction\OBOFunction.csproj -c Debug

Test

dotnet test .\test\OBOFunction.Tests\OBOFunction.Tests.csproj -c Debug

Live browser verification

The SharePoint page was verified with local Edge + Playwright against:

• https://mngenv168112.sharepoint.com/sites/gbelelenky-dev-sp/SitePages/CollabHome.aspx

Artifacts from the verification live under the session-state browser helper, not the repo.

Project layout

src/OBOFunction                  ASP.NET Core BFF proxy
spfx-sample/spfx-profile-agent   SPFx sample client
infra/                           Bicep for the proxy and observability resources
http/                            REST Client examples
test/OBOFunction.Tests           Proxy unit tests