ssh: improve error message for KeyboardInteractiveChallenge

Fixes golang/go#41823

Change-Id: I4653f23239bdf2ab472d3d15c6653b89ebf7ccd4
GitHub-Last-Rev: 179b3ee
GitHub-Pull-Request: golang#158
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/259902
Trust: Roland Shoemaker <[email protected]>
Run-TryBot: Filippo Valsorda <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Filippo Valsorda <[email protected]>

Author: packrat386

ssh/client_auth.go

@@ -471,7 +471,7 @@ func (cb KeyboardInteractiveChallenge) auth(session []byte, user string, c packe
 		}
 
 		if len(answers) != len(prompts) {
-			return authFailure, nil, errors.New("ssh: not enough answers from keyboard-interactive callback")
+			return authFailure, nil, fmt.Errorf("ssh: incorrect number of answers from keyboard-interactive callback %d (expected %d)", len(answers), len(prompts))
 		}
 		responseLength := 1 + 4
 		for _, a := range answers {