msc {

   hscale = "1.5";

   # The entities
   A, B, C, D, E;

   # Small gap before the boxes
   |||;

   # Next four on same line due to ','
   A box A [label="CLIENT", textbgcolour="#7fff7f"],
   B rbox B [label="VAULT", textbgcolour="#7fff7f"],
   C abox C [label="IDM", textbgcolour="#7fff7f"],
   D rbox D [label="SERVER", textbgcolour="#7fff7f"],
   E note E [label="Notes", textbgcolour="#7fff7f"];

   # Example of the boxes with filled backgrounds
   A => B [label="Token Request (HTTPS)"];  
   B => C [label="Auth Request (LDAPS)"];
   C => B [label="Auth Response OK (LDAPS)"];
   A <= B [label="Return client_token \nand lease_duration (HTTPS)"];
   E box E [label="\nPolicy to be associated with specific\n token are defined in Vault\n"];
   A => B [label="Sign Key Request\n (HTTPS)"];
   A <= B [label="Response Key + TTL\n (HTTPS)"];
   A => D [label="Autorization Request (SSH)"];
   A <= D [label="Server Access"];

}

mscgen -T png -i vault-ssh-sign.msc