We should rewrite strongswan authentication to reflect the structure from [[ https://docs.strongswan.org/docs/5.9/swanctl/swanctlConf.html#_secrets_ikesuffix | swanctl.conf ]]
The most important change is that more than one local/remote ID in the same auth entry should be allowed.
One of the use cases it is requirement to work with Cisco Flex VPN
Current syntax:
```
set vpn ipsec site-to-site peer OFFICE-B authentication local-id 192.0.2.1
set vpn ipsec site-to-site peer OFFICE-B authentication mode 'pre-shared-secret'
set vpn ipsec site-to-site peer OFFICE-B authentication pre-shared-secret 'SSSeeccRetT'
set vpn ipsec site-to-site peer OFFICE-B authentication remote-id 192.0.2.2
```
Proposed synta:
```
set vpn ipsec site-to-site peer OFFICE-B authentication local-id '192.0.2.1'
set vpn ipsec site-to-site peer OFFICE-B authentication mode 'pre-shared-secret'
set vpn ipsec site-to-site peer OFFICE-B authentication remote-id '192.0.2.2'
set vpn ipsec authentication psk OFFICE-B id '192.0.2.1'
set vpn ipsec authentication psk OFFICE-B id '192.0.2.2'
set vpn ipsec authentication psk OFFICE-B secret 'SSSeeccRetT'
```
Several psk's
```
set vpn ipsec site-to-site peer OFFICE-B authentication local-id '192.0.2.1'
set vpn ipsec site-to-site peer OFFICE-B authentication mode 'pre-shared-secret'
set vpn ipsec site-to-site peer OFFICE-B authentication remote-id '192.0.2.2'
set vpn ipsec authentication psk OFFICE-B1 id '192.0.2.1'
set vpn ipsec authentication psk OFFICE-B1 id '192.0.2.3'
set vpn ipsec authentication psk OFFICE-B1 id '192.0.2.4'
set vpn ipsec authentication psk OFFICE-B1 secret 'SSSeeccRetT1'
set vpn ipsec authentication psk OFFICE-B2 id '192.0.2.2'
set vpn ipsec authentication psk OFFICE-B2 id '192.0.2.5'
set vpn ipsec authentication psk OFFICE-B2 id '192.0.2.6'
set vpn ipsec authentication psk OFFICE-B2 secret 'SSSeeccRetT2'
```