Angular 6 client not authenticating against Identity Server 4

I'm trying to get my Angular 6 client to authenticate against Identity 4, but keep on getting

Showing login: User is not authenticated

My Identity Server setup is

services.AddIdentityServer()
    .AddInMemoryApiResources(new List<ApiResource>
    {
        new ApiResource("api1", "My API")
    })
    .AddInMemoryClients(new List<Client>
    {
        new Client
        {
            ClientId = "js",
            ClientName = "JavaScript Client",
            AllowedGrantTypes = GrantTypes.Implicit,
            AllowAccessTokensViaBrowser = true,
            RedirectUris = { "http://localhost:4200/callback" },
            PostLogoutRedirectUris = { "http://localhost:4200" },
            AllowedCorsOrigins =     { "http://localhost:4200" },
            AllowedScopes =
            {
                IdentityServerConstants.StandardScopes.OpenId,
                IdentityServerConstants.StandardScopes.Profile,
                "api1"
            }
        }
   })
   .AddInMemoryIdentityResources(new List<IdentityResource>
   {
       new IdentityResources.OpenId(),
       new IdentityResources.Profile()
   })
   .AddDeveloperSigningCredential();

From Angular I'm making use of oicd-client 1.5.2 that is implemented via an authentication service

export class AuthenticationService {

  private _userManager: UserManager;

  constructor() {
    this._userManager = new UserManager(this.getUserManagerSettings());
  }

  public beginAuthentication(): void {
    this._userManager.signinRedirect().then(() => {
      console.log('Signed In');
    }, error => {
      console.log(error);
    });
  }

  public endAuthentication(): void {
    this._userManager.signinRedirectCallback().then(user => {
      console.log(user);
    }, error => {
      console.log(error);
    });
  }

  private getUserManagerSettings(): UserManagerSettings {
    return {
      authority: 'http://localhost:5000',
      client_id: 'js',
      redirect_uri: 'http://localhost:4200/signin-redirect',
      response_type: 'id_token token',
      scope: 'openid profile api1',
      post_logout_redirect_uri : 'http://localhost:4200/home'
    };
  }
}

In my main component, I'm calling

signIn(): void {
    this._authenticationService.beginAuthentication();
}

The Identity Server console log displays the following

Invoking IdentityServer endpoint: IdentityServer4.Endpoints.AuthorizeEndpoint for /connect/authorize

info: IdentityServer4.Endpoints.AuthorizeEndpoint[0]
      ValidatedAuthorizeRequest
      {
        "ClientId": "js",
        "ClientName": "JavaScript Client",
        "RedirectUri": "http://localhost:4200/callback",
        "AllowedRedirectUris": [
          "http://localhost:4200/callback"
        ],
        "SubjectId": "anonymous",
        "ResponseType": "id_token token",
        "ResponseMode": "fragment",
        "GrantType": "implicit",
        "RequestedScopes": "openid profile api1",
        "State": "04ea471140f144b59495247fd6d82147",
        "Nonce": "a200fb981077440b96c8703228b75f57",
        "Raw": {
          "client_id": "js",
          "redirect_uri": "http://localhost:4200/callback",
          "response_type": "id_token token",
          "scope": "openid profile api1",
          "state": "04ea471140f144b59495247fd6d82147",
          "nonce": "a200fb981077440b96c8703228b75f57"
        }
      }
[12:03:31 Information] IdentityServer4.Endpoints.AuthorizeEndpoint
ValidatedAuthorizeRequest
{
  "ClientId": "js",
  "ClientName": "JavaScript Client",
  "RedirectUri": "http://localhost:4200/callback",
  "AllowedRedirectUris": [
    "http://localhost:4200/callback"
  ],
  "SubjectId": "anonymous",
  "ResponseType": "id_token token",
  "ResponseMode": "fragment",
  "GrantType": "implicit",
  "RequestedScopes": "openid profile api1",
  "State": "04ea471140f144b59495247fd6d82147",
  "Nonce": "a200fb981077440b96c8703228b75f57",
  "Raw": {
    "client_id": "js",
    "redirect_uri": "http://localhost:4200/callback",
    "response_type": "id_token token",
    "scope": "openid profile api1",
    "state": "04ea471140f144b59495247fd6d82147",
    "nonce": "a200fb981077440b96c8703228b75f57"
  }
}

[12:03:31 Information] IdentityServer4.ResponseHandling.AuthorizeInteractionResponseGenerator
Showing login: User is not authenticated

and then redirect to http://localhost:5000/account/login

In the constructor of the callback component, I'm calling the authentication service endAuthentication method which is calling the oidc UserManager.signinRedirectCallback method

constructor(private _authenticationService: AuthenticationService) {
    this._authenticationService.endAuthentication();
}

The callback component is never reached. Is there something that I'm missing?