Proxy and target end point both secured by oauth2

[Karuna2905]

I am working on a proxy where the first level of oauth 2 at the proxy generates a token and appends it to the header with the key Authorization. The target end point generates an oauth 2 token too. This oauth2 token needs to be appended to the header again and call a different endpoint  with the same key as Authorization. The problem is we can't have a single key as Authorization and two values. How should I approach this?