You can reference packages in a private NuGet repository using the information available here.
Once you add your private source to the config file, you can add references to your custom packages following the information outlined here.
(Additional edits from OP...)
Example project.json
{
"frameworks": {
"net46":{
"dependencies": {
"Contoso.Models": "1.2.0",
"Contoso.DAL ": "1.2.0"
}
}
}
}
project.json
is added to root folder for your function.
Example nuget.config
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<packageSources>
<add key="MyVSTSPackageManagementFeed" value="https://contoso.pkgs.visualstudio.com/_packaging/Contoso/nuget/v3/index.json" />
</packageSources>
<activePackageSource>
<add key="All" value="(Aggregate source)" />
</activePackageSource>
<packageSourceCredentials>
<MyVSTSPackageManagementFeed>
<add key="Username" value="me@contoso.com" />
<add key="ClearTextPassword" value="<MyPersonalAccessTokenHere>" />
</MyVSTSPackageManagementFeed>
</packageSourceCredentials>
</configuration>
nuget.config
is added to either the root folder for your function or if you want to use them across all of your functions, you can add it to the host level folder.