module-transaction: Add support for initiating PAM Conversations

Modules have the ability to start PAM conversations, so while the
transaction code can handle them we did not have a way to init them.
Yet.

So add some APIs allowing this, making it easier from the go side to
handle the conversations.

In this commit we only support text-based conversations, but code is
designed with the idea of supporting binary cases too.

Added the integration tests using the module that is now able to both
start conversation and handle them using Go only.

module-transaction-mock.go

@@ -7,6 +7,8 @@ package pam
 #include <stdint.h>
 #include <stdlib.h>
 #include <security/pam_modules.h>
+
+void init_pam_conv(struct pam_conv *conv, uintptr_t appdata);
 */
 import "C"
 
@@ -14,6 +16,7 @@ import (
 	"errors"
 	"fmt"
 	"runtime"
+	"runtime/cgo"
 	"testing"
 	"unsafe"
 )
@@ -110,17 +113,41 @@ func (m *mockModuleTransaction) setData(key *C.char, handle C.uintptr_t) C.int {
 	return C.int(m.RetData.Status)
 }
 
+func (m *mockModuleTransaction) getConv() (*C.struct_pam_conv, error) {
+	if m.ConversationHandler != nil {
+		conv := C.struct_pam_conv{}
+		handler := cgo.NewHandle(m.ConversationHandler)
+		C.init_pam_conv(&conv, C.uintptr_t(handler))
+		return &conv, nil
+	}
+	if C.int(m.RetData.Status) != success {
+		return nil, m.RetData.Status
+	}
+	return nil, nil
+}
+
 type mockConversationHandler struct {
-	User              string
-	ExpectedMessage   string
-	CheckEmptyMessage bool
-	ExpectedStyle     Style
-	CheckZeroStyle    bool
+	User                    string
+	PromptEchoOn            string
+	PromptEchoOff           string
+	TextInfo                string
+	ErrorMsg                string
+	ExpectedMessage         string
+	ExpectedMessagesByStyle map[Style]string
+	CheckEmptyMessage       bool
+	ExpectedStyle           Style
+	CheckZeroStyle          bool
+	IgnoreUnknownStyle      bool
 }
 
 func (c mockConversationHandler) RespondPAM(s Style, msg string) (string, error) {
-	if (c.ExpectedMessage != "" || c.CheckEmptyMessage) &&
-		msg != c.ExpectedMessage {
+	var expectedMsg = c.ExpectedMessage
+	if msg, ok := c.ExpectedMessagesByStyle[s]; ok {
+		expectedMsg = msg
+	}
+
+	if (expectedMsg != "" || c.CheckEmptyMessage) &&
+		msg != expectedMsg {
 		return "", fmt.Errorf("%w: unexpected prompt: %s vs %s",
 			ErrConv, msg, c.ExpectedMessage)
 	}
@@ -133,7 +160,20 @@ func (c mockConversationHandler) RespondPAM(s Style, msg string) (string, error)
 
 	switch s {
 	case PromptEchoOn:
-		return c.User, nil
+		if c.User != "" {
+			return c.User, nil
+		}
+		return c.PromptEchoOn, nil
+	case PromptEchoOff:
+		return c.PromptEchoOff, nil
+	case TextInfo:
+		return c.TextInfo, nil
+	case ErrorMsg:
+		return c.ErrorMsg, nil
+	}
+
+	if c.IgnoreUnknownStyle {
+		return c.ExpectedMessage, nil
 	}
 
 	return "", fmt.Errorf("%w: unhandled style: %v", ErrConv, s)