Implementation for SEP-2350 Client-side scope accumulation in step-up authorization (#1591)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Tarek Mahmoud Sayed <tarekms@microsoft.com>

.github/skills/run-conformance-from-branch/SKILL.md

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+---
+name: run-conformance-from-branch
+description: Run MCP conformance tests in the C# SDK against a conformance branch (including forks) instead of the published npm version, then restore pinned dependencies.
+compatibility: Requires npm, node, and dotnet SDK. Uses the csharp-sdk repo package.json/package-lock.json and tests/ModelContextProtocol.AspNetCore.Tests.
+---
+
+# Run Conformance From Branch
+
+Run C# SDK conformance tests against an unpublished `modelcontextprotocol/conformance` branch (including branches in forks).
+
+## Use Cases
+
+- Validate a conformance PR before it is published to npm
+- Validate C# SDK behavior against a fork with custom scenario changes
+- Reproduce failures caused by conformance changes
+
+## Safety / Repo Hygiene
+
+1. Start from a clean git state.
+2. Commit or stash local changes first.
+3. Restore pinned dependencies when done (`npm ci`).
+
+## Inputs
+
+- **Source type**: `upstream-branch` or `fork-branch`
+- **Source locator**:
+  - Upstream branch: `modelcontextprotocol/conformance#<branch>`
+  - Fork branch: `<owner>/conformance#<branch>`
+- **Scenario** (optional): e.g. `auth/scope-step-up`
+
+## Workflows
+
+### A) Install directly from GitHub branch (upstream or fork)
+
+From `csharp-sdk` root:
+
+```bash
+npm install --no-save @modelcontextprotocol/conformance@github:<owner>/conformance#<branch>
+```
+
+Examples:
+
+```bash
+npm install --no-save @modelcontextprotocol/conformance@github:modelcontextprotocol/conformance#main
+npm install --no-save @modelcontextprotocol/conformance@github:myuser/conformance#sep-2350-check
+```
+
+## Run Tests
+
+### Run client conformance tests with dotnet test filter:
+
+```bash
+dotnet test tests/ModelContextProtocol.AspNetCore.Tests/ModelContextProtocol.AspNetCore.Tests.csproj -f net10.0 --filter "FullyQualifiedName~ClientConformanceTests"
+```
+
+### Run server conformance tests with dotnet test filter:
+
+```bash
+dotnet test tests/ModelContextProtocol.AspNetCore.Tests/ModelContextProtocol.AspNetCore.Tests.csproj -f net10.0 --filter "FullyQualifiedName~ServerConformanceTests"
+```
+
+## Reporting
+
+Always report:
+
+1. Installed conformance source (`npm ls @modelcontextprotocol/conformance --depth=0`)
+2. Scenario results (pass/fail/warnings)
+3. Any new check IDs observed (for traceability)
+
+## Cleanup / Restore
+
+Return repo to pinned dependency state:
+
+```bash
+npm ci
+```