SFTP Connector | Version 2.0.0 and above doesn't work with Identity File in .ppk format

SYMPTOM

You have a mule application that uses the SFTP connector 2.0.0 version and above (Apache mina library is used) and the authentication is the "PUBLIC_KEY" method using Identity File in .ppk format. The app fails with the below warning if the preferredAuthenticationMethods="#[['PUBLIC_KEY']]"

org.mule.runtime.api.connection.ConnectionException: Could not establish SFTP connection with host: '<host>' at port: '<port>' - No more authentication methods available
Caused by: org.mule.extension.sftp.internal.exception.SftpConnectionException: Could not establish SFTP connection with host: '<host>' at port: '<port>' - No more authentication methods available
Caused by: org.mule.runtime.extension.api.exception.ModuleException: org.apache.sshd.common.SshException: No more authentication methods available
Caused by: org.apache.sshd.common.SshException: No more authentication methods available

And fails with the below error if nothing is specified in the "preferredAuthenticationMethods".

Error was: Could not establish SFTP connection with host: '' at port: '22' - [ssh-connection]: Failed to get operation result within specified timeout: 10000 msec
org.mule.runtime.api.connection.ConnectionException: Could not establish SFTP connection with host: '' at port: '22' - [ssh-connection]: Failed to get operation result within specified timeout: 10000 msec
Caused by: org.mule.extension.sftp.internal.exception.SftpConnectionException: Could not establish SFTP connection with host: '' at port: '22' - [ssh-connection]: Failed to get operation result within specified timeout: 10000 msec
Caused by: org.mule.runtime.extension.api.exception.ModuleException: org.apache.sshd.common.SshException: [ssh-connection]: Failed to get operation result within specified timeout: 10000 msec
Caused by: org.apache.sshd.common.SshException: [ssh-connection]: Failed to get operation result within specified timeout: 10000 msec

Below is the configuration used.

<sftp:config name="SFTP_Config" doc:name="SFTP Config" doc:id="34cf9b32-d3de-4171-b6e9-36dc0b25e7c0" >
<sftp:connection host="${host}" username="${user}" identityFile="${app.home}/${file-ppk}" passphrase="${pwd}" port="${port}" workingDir="${root-folder}" preferredAuthenticationMethods="#[['PUBLIC_KEY']]">
</sftp:connection>
</sftp:config>

CAUSE

This is due to the limitation with the Apache mina library which doesn't work with the .ppk file format. Our connector documentation also mentions that ssh-keygen’s OpenSSH PKI format is not accepted.
https://docs.mulesoft.com/sftp-connector/latest/sftp-documentation#config_connection

An identity file location for a PKI private key.
ssh-keygen’s OpenSSH PKI format is not accepted. You can use argument "-m PEM".

SOLUTION

Download PuTTYgen:
If you don't have PuTTYgen installed, you can download it as part of the PuTTY suite from the official website: PuTTY Download Page
https://www.putty.org/

Open PuTTYgen:

Run PuTTYgen.
Click on the "Load" button.
Load the .ppk Private Key:

In the file dialog, select the option to display files with all extensions.
Locate and select your .ppk private key file.
Click "Open."
Convert and Save as PEM:

Once the .ppk file is loaded, click on the "Conversions" menu.
Choose "Export OpenSSH Key."
Save the file with a .pem extension.