Windows 10 sshd - passwordless incoming ssh demands a password

I am attempting to set up passwordless, passphraseless ssh from a Linux Mint 19.1 host to a Windows 10 host. The Windows 10 host has OpenSSH_for_Windows_7.7p1 on it. This is Microsoft's OpenSSH port.

I am able to set this up for administrator accounts, but unprivileged accounts are not working for me. Administrator accounts are done differently.

I've tried a large number of different things, but here's the one I feel should work, and what goes wrong with it:

I create a /Users/Alden Stromberg/.ssh/authorized_keys file with mkdir and echo > (or mkdir and cygwin vi - same result).

Then I use OpenSSHUtils to attempt to set the correct permissions:

PS C:\Users\Alden Stromberg\.ssh> Import-Module 'C:\Program Files\WindowsPowerShell\Modules\OpenSSHUtils\0.0.2.0\OpenSSHUtils.psd1'

PS C:\Users\Alden Stromberg\.ssh> Repair-AuthorizedKeyPermission .\authorized_keys                                                   
  [*] .\authorized_keys 

'NT AUTHORITY\SYSTEM' has the following access to '.\authorized_keys': 'Deny'-'ExecuteFile'.
Shall I make it Allow FullControl?
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help (default is "Y"):  
Exception calling "SetAccessRule" with "1" argument(s): "This access control list is not in canonical form and therefore cannot be  
modified."
At C:\Program Files\WindowsPowerShell\Modules\OpenSSHUtils\0.0.2.0\OpenSSHUtils.psm1:399 char:17
+                 $acl.SetAccessRule($ace)
+                 ~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : InvalidOperationException

'NT AUTHORITY\SYSTEM' now has FullControl access to '.\authorized_keys'. 

'DESKTOP-A31M9SV\None' should not have access to '.\authorized_keys'..
Shall I remove this access?
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help (default is "Y"):
Exception calling "RemoveAccessRule" with "1" argument(s): "This access control list is not in canonical form and therefore cannot  
be modified."
At C:\Program Files\WindowsPowerShell\Modules\OpenSSHUtils\0.0.2.0\OpenSSHUtils.psm1:490 char:20
+                 if(-not ($acl.RemoveAccessRule($ace)))
+                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : InvalidOperationException


'Everyone' should not have access to '.\authorized_keys'..
Shall I remove this access?
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help (default is "Y"):  
Exception calling "RemoveAccessRule" with "1" argument(s): "This access control list is not in canonical form and therefore cannot  
be modified."
At C:\Program Files\WindowsPowerShell\Modules\OpenSSHUtils\0.0.2.0\OpenSSHUtils.psm1:490 char:20
+                 if(-not ($acl.RemoveAccessRule($ace)))
+                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : InvalidOperationException


'NT SERVICE\sshd' needs Read access to '.\authorized_keys'.
Shall I make the above change?
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help (default is "Y"):
Exception calling "AddAccessRule" with "1" argument(s): "This access control list is not in canonical form and therefore cannot be  
modified."
At C:\Program Files\WindowsPowerShell\Modules\OpenSSHUtils\0.0.2.0\OpenSSHUtils.psm1:564 char:21
+                     $acl.AddAccessRule($ace)
+                     ~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : InvalidOperationException

'NT SERVICE\sshd' now has Read access to '.\authorized_keys'.
Set-Acl : The process does not possess the 'SeSecurityPrivilege' privilege which is required for this operation.
At C:\Program Files\WindowsPowerShell\Modules\OpenSSHUtils\0.0.2.0\OpenSSHUtils.psm1:582 char:9 
+         Set-Acl -Path $FilePath -AclObject $acl -Confirm:$false
+         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : PermissionDenied: (C:\Users\Alden ...authorized_keys:String) [Set-Acl], PrivilegeNotHeldException      
    + FullyQualifiedErrorId : System.Security.AccessControl.PrivilegeNotHeldException,Microsoft.PowerShell.Commands.SetAclCommand    

      Repaired permissions

Hoping to fix the noncanonical ACL, I tried:

icacls.exe .\authorized_keys /reset /T /C /L /Q

...but subsequently rerunning Repair-AuthorizedKeyPermission produces no joy.

What am I doing wrong? Is 0.0.2.0\OpenSSHUtils.psm1 out of date?

For the sake of completeness, here's what worked for administrator accounts:

get-acl c:\ProgramData\ssh\ssh_host_dsa_key | set-acl c:\ProgramData\ssh\administrators_authorized_keys

Thanks!

What fixed this issue for me was to comment out these two lines at the end of the C:\ProgramData\ssh\sshd_config file:

Match Group administrators
      AuthorizedKeysFile __PROGRAMDATA__/ssh/administrators_authorized_keys

Then restart sshd. After that (and adding the pub key to ~/.ssh/authorized_keys and making sure that file had the correct perms) I was not prompted for a password anymore.

One way of getting passwordless authentication working for non-administrator accounts, is described at: https://www.techpaste.com/2015/06/windows-ssh-server-setup-and-configuration/

In short, put these in your sshd_config, uncommenting preexisting entries as needed, found under c:\ProgramData\ssh\

PermitRootLogin yes
StrictModes no
RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys
IgnoreUserKnownHosts yes

Then net stop sshd and net start sshd.

This probably means that your authorized_keys is readable by everyone on the computer, but at least it works.