upgrade deps; rewrite smtp session

vendor/gitlab.com/etke.cc/go/secgen/README.md

@@ -3,6 +3,7 @@
 Secrets generator, supported types:
 
 * Passwords
+* Random bytes
 * ED25519 SSH keypairs
 
 Simple go environment variables reader, for env-based configs
@@ -10,6 +11,8 @@ Simple go environment variables reader, for env-based configs
 ```go
 // password
 securePassword := secgen.Password(64)
+// base64-encode random bytes (openssl rand -base64 replacement)
+randomBytes := secgen.Base64Bytes(64)
 
 // ssh key
 publicSSHkey, privateSSHkey, err := secgen.Keypair()