Add handeling for open ssh format

tests/assert-env-unset.sh

@@ -21,3 +21,6 @@ assert_env_unset "FILE_MULTILINE_SECRET"
 assert_env_unset "SECRET_WITH_FILE"
 assert_env_unset "SECRET_WITH_FILE_IN_SECTION"
 assert_env_unset "DOUBLE_SECTION_SECRET"
+
+assert_env_unset "SSH_PRIVATE_KEY"
+assert_env_unset "SSH_PRIVATE_KEY_OPENSSH"

tests/assert-ssh-keys.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+set -e
+
+# SSH_PRIVATE_KEY: any private key format
+v="$(printenv SSH_PRIVATE_KEY)"
+if [ -z "$v" ]; then
+  echo "SSH_PRIVATE_KEY is not set"
+  exit 1
+fi
+if ! echo "$v" | head -1 | grep -qE -- '^-----BEGIN (RSA |EC |OPENSSH )?PRIVATE KEY-----'; then
+  echo "SSH_PRIVATE_KEY does not start with a private key header"
+  exit 1
+fi
+if ! echo "$v" | tail -1 | grep -qE -- '-----END (RSA |EC |OPENSSH )?PRIVATE KEY-----$'; then
+  echo "SSH_PRIVATE_KEY does not end with a private key footer"
+  exit 1
+fi
+echo "SSH_PRIVATE_KEY has valid key format"
+
+# SSH_PRIVATE_KEY_OPENSSH: OpenSSH format only
+v="$(printenv SSH_PRIVATE_KEY_OPENSSH)"
+if [ -z "$v" ]; then
+  echo "SSH_PRIVATE_KEY_OPENSSH is not set"
+  exit 1
+fi
+if ! echo "$v" | head -1 | grep -q -- '-----BEGIN OPENSSH PRIVATE KEY-----'; then
+  echo "SSH_PRIVATE_KEY_OPENSSH is not in OpenSSH format"
+  exit 1
+fi
+if ! echo "$v" | tail -1 | grep -q -- '-----END OPENSSH PRIVATE KEY-----$'; then
+  echo "SSH_PRIVATE_KEY_OPENSSH does not end with OpenSSH private key footer"
+  exit 1
+fi
+echo "SSH_PRIVATE_KEY_OPENSSH has valid OpenSSH key format"