Consider ability to force CK change

[jessepeterson]

The fix for #1 guarded against uploading tokens with a differing consumer key. However if the CK legitimately changes there may be a need to allow "forcing" replacing the OAuth tokens for a given DEP name.

[jessepeterson]

Had to do this patch (to disable CK replacement check) to replace a token that had a different account replace the token:

diff --git a/cmd/depserver/main.go b/cmd/depserver/main.go
index 89824b7..ea01b2b 100644
--- a/cmd/depserver/main.go
+++ b/cmd/depserver/main.go
@@ -72,7 +72,7 @@ func main() {
        }
 
        tokensMux := dephttp.NewMethodMux()
-       tokensMux.Handle("PUT", api.StoreAuthTokensHandler(api.NewCKCheck(storage), logger.With("handler", "store-auth-tokens")))
+       tokensMux.Handle("PUT", api.StoreAuthTokensHandler(storage, logger.With("handler", "store-auth-tokens")))
        tokensMux.Handle("GET", api.RetrieveAuthTokensHandler(storage, logger.With("handler", "retrieve-auth-tokens")))
        handleStrippedAPI(tokensMux, endpointTokens)
 
@@ -83,7 +83,7 @@ func main() {
 
        tokenPKIMux := dephttp.NewMethodMux()
        tokenPKIMux.Handle("GET", api.GetCertTokenPKIHandler(storage, logger.With("handler", "get-token-pki")))
-       tokenPKIMux.Handle("PUT", api.DecryptTokenPKIHandler(storage, api.NewCKCheck(storage), logger.With("handler", "put-token-pki")))
+       tokenPKIMux.Handle("PUT", api.DecryptTokenPKIHandler(storage, storage, logger.With("handler", "put-token-pki")))
        handleStrippedAPI(tokenPKIMux, endpointTokenPKI)
 
        assignerMux := dephttp.NewMethodMux()