RefreshTokenClient doesnt use client_secret and that causes error in DelegatedTokenClient

[ViktorFefilov]

flow:

• get authorization_code
• initialize DelegatedTokenCredentials with authorization_code
• do request to resource A with DelegatedTokenCredentials (OK)
• do request to resource B with DelegatedTokenCredentials (fail with message OAuth2 Authorization code was already redeemed)

But actually bug is not about authorization_code. First exception occurs in RefreshTokenClient in method refreshToken but he just returns null in catch block and by this reason DelegatedTokenCredentials is trying to use authorization_code to acquire access token

my fix for this issue you can find in my fork

[anuchandy]

linking the fix that @ViktorFefilov mentioned ViktorFefilov@7ec7e79

[jianghaolu]

@ViktorFefilov Thanks for sharing your fix with us. I'm planning to take it in this PR: #632