feat: return validation failed error if captcha request was not json (#1815)

Returns HTTP 400 with the validation failed error code if the request
body sent to the server when CAPTCHA verification is enabled was not
JSON or couldn't be parsed into JSON.

Author: hf

internal/api/middleware.go

@@ -118,6 +118,10 @@ func (a *API) verifyCaptcha(w http.ResponseWriter, req *http.Request) (context.C
 
 	verificationResult, err := security.VerifyRequest(req, strings.TrimSpace(config.Security.Captcha.Secret), config.Security.Captcha.Provider)
 	if err != nil {
+		if strings.Contains(err.Error(), "request body was not JSON") {
+			return nil, badRequestError(ErrorCodeValidationFailed, "Request body for CAPTCHA verification was not a valid JSON object")
+		}
+
 		return nil, internalServerError("captcha verification process failed").WithInternalError(err)
 	}