ASP.NET Core "Unable to configure HTTPS endpoint. No server certificate was specified" in CI

Kestrel tried to bind an https endpoint and looked for the ASP.NET Core developer certificate, which does not exist on a fresh CI runner. Bind to http in CI, or generate and trust a dev cert first.

What this error means

The app fails to start in CI with "Unable to configure HTTPS endpoint. No server certificate was specified, and the default developer certificate could not be found or is out of date." Locally it works because Visual Studio installed a dev cert.

.NET

System.InvalidOperationException: Unable to configure HTTPS endpoint. No server
certificate was specified, and the default developer certificate could not be found
or is out of date. To generate a developer certificate run 'dotnet dev-certs https'.

Common causes

No developer certificate on the runner

The default Kestrel https binding needs the ASP.NET Core dev cert. A clean runner never ran dotnet dev-certs https --trust, so the certificate is missing.

launchSettings binds https by default

Your launchSettings.json or applicationUrl defaults to https://localhost:..., so CI inherits an https endpoint it cannot secure.

How to fix it

Bind to http only in CI

Set ASPNETCORE_URLS to an http address in the CI step.
Do not rely on launchSettings in CI (it is a local dev file, not read by dotnet run in all hosts).
Point integration tests at the http endpoint.

.github/workflows/ci.yml

env:
  ASPNETCORE_URLS: http://localhost:5000
  ASPNETCORE_ENVIRONMENT: Development

Generate and trust a dev cert when https is required

If a test genuinely needs https, create the developer certificate before starting the app.

Terminal

dotnet dev-certs https
dotnet dev-certs https --trust

How to prevent it

Use http endpoints for CI runs; reserve https for environments with real certificates.
Set ASPNETCORE_URLS explicitly instead of depending on launchSettings.json.
Terminate TLS at a proxy or ingress in production rather than in Kestrel dev certs.