title: System.IdentityModel.Metadata and X509SecurityToken not available in ASP.NET Core
body: <p>I'm currently trying to get signing keys from Azure Active Directory based on the <a href="https://docs.microsoft.com/en-us/azure/active-directory/develop/active-directory-signing-key-rollover" rel="nofollow noreferrer">signing key rollover guide</a> over at Microsoft docs in order to authenticate HTTP requests on an ASP.NET Core Web API endpoint I'm developing. </p>
  
  <p>Although I migrated the source code shown in the article it doesn't seem like some references and classes are available in ASP.NET Core web apps such as <code>System.IdentityModel.Metadata</code> and classes like <code>X509SecurityToken</code>, <code>MetadataSerializer</code>, <code>EntityDescriptor</code> and <code>X509RawDataKeyIdentifierClause</code>. </p>
  
  <p><a href="https://i.stack.imgur.com/s9h5f.jpg" rel="nofollow noreferrer">Source code with types not found</a></p>
  
  <p>I already searched on NuGet, but it doesn't seem like packages are available for System.IdentityModel and I'm not able to reference system assemblies in ASP.NET Core neither. </p>
  
  <p>Which libraries shall I use in ASP.NET Core instead?</p>