Disable redirect of HTTP request to a HTTPS Minio server (#4454)

Fixes #4452

cmd/api-errors.go

@@ -149,6 +149,7 @@ const (
 	ErrAdminInvalidAccessKey
 	ErrAdminInvalidSecretKey
 	ErrAdminConfigNoQuorum
+	ErrInsecureClientRequest
 )
 
 // error code to APIError structure, these fields carry respective
@@ -618,6 +619,11 @@ var errorCodeResponse = map[APIErrorCode]APIError{
 		Description:    "Configuration update failed because server quorum was not met",
 		HTTPStatusCode: http.StatusServiceUnavailable,
 	},
+	ErrInsecureClientRequest: {
+		Code:           "XMinioInsecureClientRequest",
+		Description:    "Cannot respond to plain-text request from TLS-encrypted server",
+		HTTPStatusCode: http.StatusBadRequest,
+	},
 
 	// Add your error structure here.
 }