check for null redirectUri to prevent NullReferenceException and throw a better error
Fixes build errors for ReadAsAsync in Oidc project

Fixes were to remove reference to rc nuget packages and update to latest
Resolves runtime error due to Jwt not 3.0.0

At runtime the CodeFlowClient app was failing to deserialize the JWT due
to the Thinktecture.IdentityModel.Oidc.dll referencing
System.IdentityModel.Tokens.Jwt nuget 3.0.0 but the CodeFlowClient was
using 1.0.0