Nuget Trusted Publishing skill

NuGet Trusted Publishing Setup

Set up NuGet trusted publishing on a GitHub Actions repo. Replaces long-lived API keys with OIDC-based short-lived tokens — no secrets to rotate or leak.

Prerequisites

• GitHub Actions — this skill covers GitHub Actions setup only
• nuget.org account — the user needs access to create trusted publishing policies

When to Use This Skill

Use this skill when:

• Setting up trusted publishing for a NuGet package
• Migrating from secrets.NUGET_API_KEY to OIDC-based publishing
• Asked about keyless or secure NuGet publishing
• Creating a new NuGet publish workflow from scratch
• Asked to "remove NuGet API key" or "use NuGet/login"
• Setting up publishing for a dotnet tool, MCP server, or template package
• Asked about NuGet/login@v1 or id-token: write

Safety Rules

⚠️ Bail-out rule: If any phase fails after one fix attempt on an infrastructure/auth issue, stop and ask the user. Don't loop on environment problems.

⚠️ Never delete or overwrite without confirmation: Removing API key secrets, deleting tags/releases, removing workflow steps, or changing package IDs. NuGet package IDs are permanent — mistakes can't be undone.

Process

Fast-path for greenfield repos: When the user has a simple setup (one packable project, no existing publish workflow), don't gate on multi-turn assessment. Combine phases: create the workflow immediately, include nuget.org policy guidance, local pack recommendation, and filename-matching warning all in one response. The full phased process below is for complex or migration scenarios.

Phase 1: Assess

Inspect the repo and report findings before making any changes.

1. Find and classify packable projects — check .csproj files and Directory.Build.props (package metadata is often set repo-wide). Classify in this order (earlier matches win):

   • <PackageType>Template</PackageType> → Template
   • <PackageType>McpServer</PackageType> → MCP server (also a dotnet tool)
   • <PackAsTool>true</PackAsTool> → Dotnet tool
   • Class library (IsPackable=true or no OutputType) → Library
   • <OutputType>Exe</OutputType> with <IsPackable>true</IsPackable> → Application package (not a tool, but still publishable)
   • <OutputType>Exe</OutputType> without PackAsTool or IsPackable → Not packable by default (ask user if they intend to publish it)

2. Validate structure for each project's type:

   Type	Required
   All	PackageId, Version (in .csproj or Directory.Build.props)
   Dotnet tool	PackAsTool (required); ToolCommandName (optional but recommended — defaults to assembly name)
   MCP server	PackageType=McpServer, .mcp/server.json included in package
   Template	PackageType=Template, .template.config/template.json under content dir

3. Find existing publish workflows in .github/workflows/ — look for dotnet nuget push, nuget push, or dotnet pack.

4. Check version consistency — for MCP servers, verify .csproj <Version> matches both server.json version fields (root version and packages[].version). Flag any mismatch.

5. Report findings to the user: classification, missing properties, version mismatches, existing workflows. For multi-project repos, note whether one workflow or separate workflows per package are needed. Offer to fix gaps — use ask_user before modifying project files.

❌ See references/package-types.md for per-type details and required properties.

Phase 2: Local Verification

Pack and verify locally before touching nuget.org — publishing errors waste a permanent version number.

⚠️ Always mention this step, even if you defer running it. Tell the user: "Before your first publish, run dotnet pack -c Release -o ./artifacts to verify the .nupkg is created correctly."

1. dotnet pack -c Release -o ./artifacts — verify .nupkg is created
2. For tools/MCP servers: install from ./artifacts, run --help, uninstall
3. For libraries: inspect the .nupkg contents (it's a zip)

Phase 3: nuget.org Policy

This phase requires the user to act on nuget.org — guide them with exact values.

1. Determine the repo owner, repo name, and the workflow filename that will publish.

   ❌ The policy requires the exact workflow filename (e.g., publish.yml or publish.yaml) — just the filename, no path prefix. Matching is case-insensitive. Don't use the workflow name: field.

2. Guide the user to create the trusted publishing policy:

   Go to nuget.org/account/trustedpublishing → Add policy

   • Repository Owner: {owner}
   • Repository: {repo}
   • Workflow File: {filename}.yml
   • Environment: release (only if the workflow uses environment:; leave blank otherwise)

   Policy ownership: the user chooses individual account or organization. Org-owned policies apply to all packages owned by that org.

   For private repos: policy is "temporarily active" for 7 days — becomes permanent after the first successful publish.

3. Guide the user to create a GitHub Environment (recommended but optional — provides secret scoping + approval gates):

   Repo Settings → Environments → New environment → release

   Add environment secret: Name = NUGET_USER, Value = nuget.org username (NOT email)

   Optional: add Required reviewers for an approval gate.

⚠️ Wait for the user to confirm they've created the policy before asking them to remove old API keys/secrets or before attempting to run/publish with the workflow. Drafting or showing the workflow file itself is OK before confirmation.

Phase 4: Workflow Setup

Create or modify the publish workflow. The workflow must always be created or shown in your response — you may draft/show it even if the nuget.org policy is not yet confirmed, but do not guide the user to actually run/publish or remove old secrets until after confirmation.

Greenfield: Create publish.yml from the template in references/publish-workflow.md. Adapt .NET version, project path, and environment name. Ensure your output explicitly mentions id-token: write and NuGet/login@v1.

Migration (existing workflow with API key): Modify in place —

1. Add OIDC permission and environment to the publishing job:

   jobs:
     publish:
       environment: release
       permissions:
         id-token: write     # Required — without this, NuGet/login fails with 403
         contents: read      # Explicit — setting permissions overrides defaults
   

2. Add the NuGet login step before push:

   - name: NuGet login (OIDC)
     id: login
     uses: NuGet/login@v1
     with:
       user: ${{ secrets.NUGET_USER }}  # nuget.org profile name, NOT email
   

3. Replace the API key in the push step:

   --api-key ${{ steps.login.outputs.NUGET_API_KEY }} --skip-duplicate
   

4. Verify: Ask the user to trigger a publish and confirm the package appears on nuget.org.

❌ Don't delete the old API key secret until trusted publishing is verified. Removing it is a one-way door — wait for confirmation.

Troubleshooting

Problem	Cause	Fix
NuGet/login 403	Missing id-token: write	Add to job permissions
"no matching policy"	Workflow filename mismatch	Verify exact filename on nuget.org
Push unauthorized	Package not owned by policy account	Check policy owner on nuget.org
Token expired	Login step >1hr before push	Move NuGet/login closer to push
"temporarily active" policy	Private repo, first publish pending	Publish within 7 days
already_exists on push	Re-running same version	Add --skip-duplicate
GitHub Release 422	Duplicate release for tag	Delete conflicting release (confirm first)
Re-run uses wrong YAML	gh run rerun replays original commit's YAML	Delete obstacle, re-run — never re-tag

⚠️ If any blocker persists after one fix attempt, stop and ask the user.

References

• Package type details: references/package-types.md — detection logic, required properties, minimal .csproj examples
• Publish workflow template: references/publish-workflow.md — complete tag-triggered workflow ready to adapt
• Microsoft docs: NuGet Trusted Publishing