Public key import on SFTP server for third party application communication

Let us assume, we have 3 entities: 1) Alfresco 2) SFTP location/FTP server 3) SAP system
Now, we have a functional user/SSO configured (whose credentials OR public key - ppk/pem file we use to connect via WinSCP/Putty).
Now, using the same key, SAP needs to connect to this SFTP server and put/upload files on a fixed/shared location.

Steps to be performed:
1) Provide the public key (ppk or pem file) to SAP for importing on their side.
2) SAP will provide a public key (ex: sap0x...dev.pub).
3) Place this file under the .ssh folder of the configured functional user home folder: (ex: /home/5045xxx23/.ssh)
4) If .ssh folder does not exist, create it. 
NOTE: If you don't have the rights with your user, do it with root user (sudo -s). Later on, you can change the owner using : chown <new_owner> <file_name>
5) Use the following command to copy the key (content) of sap0x..dev.pub into authorized_keys file. : cat sap0x...dev.pub >> authorized_keys
NOTE: If authorized_key file doesnot exist, create it.
6) Set the following permissions:
/home/5045xxx23 : 0755
.ssh : 0755
.bash_history : 0600
sap0x...dev.pub : 0644
authorized_keys : 0644

NOTE: Delete any additional files from .ssh folder (ex: .ppk file, authorized_keys.old , id_rsa.pub , any public key backup file with .BAK extension, etc)

Also, check twice the functional user/SSO that SAP team is connecting to.
If SAP team is not able to connect to Alfresco, then one issue can be : The configured functional user/SSO for this SFTP (ex: alfrescoFtpDev) might be different from what SAP is using. 
If this functional SSO folder is not existing under /home directory, then create the following with root user:
/home/502.xxx.6
/home/502.xxx.6/.ssh
Copy the files (authorized_keys & sap0x...dev.pub) from other SSO folder (/home/5045xxx23/.ssh) to this new location - /home/502.xxx.6/.ssh/
Set the permissions as per mentioned above.