dev-certificates on Linux -- how to get dotnet-to-dotnet comms to work?

### Description
I have an asp.net core application with a self-hosted IdentityServer component. I can convince a browser (Chrome and Firefox) to visit the site, but I'm having trouble getting the IdentityServer component to be able to talk back to localhost due to certificate errors, specifically:
```
fail: Microsoft.AspNetCore.Authentication.JwtBearer.JwtBearerHandler[3]
Exception occurred while processing message.
System.InvalidOperationException: IDX20803: Unable to obtain configuration from: 'https://localhost:44303/.well-known/openid-configuration'. ---> System.IO.IOException: IDX20804: Unable to retrieve document from: 'https://localhost:44303/.well-known/openid-configuration'. ---> System.Net.Http.HttpRequestException: The SSL connection could not be established, see inner exception. ---> System.Security.Authentication.AuthenticationException: The remote certificate is invalid according to the validation procedure.
```
I realise that certificate installation can differ from distro to distro, however, I've tried this first on my (more native) Gentoo, and also in an Ubuntu vm:

1. export the dev cert to a pfx with `dotnet dev-certs https -ep /tmp/dnc.pfx -p SomePassword`
2. extract the crt from the pfx with `openssl pkcs12 -in /tmp/dnc.pfx -clcerts -nokeys -out /tmp/dnc.crt`
3. copy to /usr/local/share/ca-certificates and run update-ca-certificates. In both cases (Gentoo and Ubuntu), see a message about 1 added certificate
3.5 in the case of Gentoo, I was also able to use certutil to install the crt into my ~/.pki/nssdb; in the case of Ubuntu, this dir does not exist and I'm not sure how to bootstrap it
4. Fire up the asp.net site with angular frontend -- on Gentoo, where certutil worked, Chrome happily visits the site; on both (iirc) I had to add a security exception for Firefox and store, but could get to the site.
5. Attempts to log in fail because all auth requests go through the primary api, which then attempts to contact the same host/port (localhost:44303) for IdentityServer comms -- and that's where the failure occurs with the message above: I can get no further

### To Reproduce
Set up an asp.net core project with self-hosted IdentityServer on Linux, such that the config for identity server points back to the same hosting application, using dev certs. Any route requiring authorization will result in a 500 error with the above logging in place. Using `dotnet dev-certs https --trust` on Windows, same code, no problem.

### Expected behavior
I expect to be able to get dotnet-to-dotnet comms working with the dev cert. I'm probably missing something )':

Ubuntu dotnet info:
.NET Core SDK (reflecting any global.json):
Version: 2.2.103
Commit: 8edbc2570a

Runtime Environment:
OS Name: ubuntu
OS Version: 18.10
OS Platform: Linux
RID: ubuntu.18.10-x64
Base Path: /usr/share/dotnet/sdk/2.2.103/

Host (useful for support):
Version: 2.2.1
Commit: 878dd11e62

.NET Core SDKs installed:
2.2.103 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.2.1 [/usr/share/dotnet/shared/Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.2.1 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.2.1 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
https://aka.ms/dotnet-download

Gentoo dotnet info:
.NET Core SDK (reflecting any global.json):
Version: 2.2.103
Commit: 8edbc2570a

Runtime Environment:
OS Name: ubuntu
OS Version: 18.10
OS Platform: Linux
RID: ubuntu.18.10-x64
Base Path: /usr/share/dotnet/sdk/2.2.103/

Host (useful for support):
Version: 2.2.1
Commit: 878dd11e62

.NET Core SDKs installed:
2.2.103 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.2.1 [/usr/share/dotnet/shared/Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.2.1 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.2.1 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
https://aka.ms/dotnet-download

I have also tried with dotnet binaries from https://dotnet.microsoft.com/download/thank-you/dotnet-sdk-2.2.103-linux-x64-binaries