Add 'env_var_' prefix option for handling secrets

README.md

@@ -297,17 +297,26 @@ export NDFC_SW_USERNAME=admin
 export NDFC_SW_PASSWORD=Admin_123
 ```
 
+#### Handling Secrets
+
+This collection supports two options to securely handle secrets in the NaC VXLAN data model such as passwords and authentication keys:
+
+* **🔐 Ansible Vault**: Encrypts credentials
+* **✅ Environment Variables**: Resolves secrets from environment variables
+
+**📖 Guide**: [Handling Secrets Guide](docs/Handling_Secrets_Guide.md)
+
 ##### Switch Credential Management
 
-This collection supports flexible credential management for network switches with three security levels:
+For switch credentials specifically, this collection supports flexible credential management with three security levels:
 
 * **🔐 Ansible Vault**: Encrypted credentials for production deployments
 * **✅ Environment Variables**: Secure credential injection for CI/CD pipelines
 * **⚠️ Plain Text**: Simple credentials for lab testing only
 
-The system supports both switch-specific credentials and group-level defaults with automatic fallback. Environment variable lookups can be configured in group_vars for enhanced security and automation compatibility.
+NaC VXLAN supports both switch-specific credentials and group-level defaults with automatic fallback. Environment variable lookups can be configured in group_vars for enhanced security and automation compatibility.
 
-**📖 Complete Guide**: [Switch Credentials Configuration](docs/SWITCH_CREDENTIALS_GUIDE.md)
+**📖 Guide**: [Switch Credentials Configuration](docs/SWITCH_CREDENTIALS_GUIDE.md)
 
 ## Quick Start Guide
 

docs/Handling_Secrets_Guide.md

@@ -0,0 +1,136 @@
+# Handling Secrets Guide
+
+This guide describes how to manage secrets such as passwords and authentication keys in the Network as Code VXLAN data model. There are two mechanisms available:
+
+1. **Ansible Vault** - Encrypts entire variable values at rest.
+2. **Environment Variable Lookup (`env_var_`)** - Resolves secrets from environment variables at runtime. Suitable for CI/CD integration.
+
+Both approaches ensure that plaintext secrets are not visible in the data YAML files. The key difference is that Ansible Vault encrypts whole values while `env_var_` replaces individual strings — making `env_var_` the only option for secrets embedded in freeform configuration blocks.
+
+---
+
+## Ansible Vault
+
+[Ansible Vault](https://docs.ansible.com/ansible/latest/vault_guide/index.html) encrypts sensitive data so it can be stored safely in data files. Encrypted values are decrypted automatically at playbook runtime when a vault password is provided.
+
+### Encrypting a Value
+
+```bash
+ansible-vault encrypt_string 'MySecretPassword' --name 'authentication_key'
+```
+
+This produces an encrypted variable which you can paste into your data files:
+
+```yaml
+vxlan:
+  underlay:
+    bgp:
+      authentication_enable: true
+      authentication_key_type: 3
+      authentication_key: !vault |
+        $ANSIBLE_VAULT;1.1;AES256
+        61626364656667686970...
+```
+
+### Running Playbooks with Vault
+
+```bash
+# Prompt for vault password
+ansible-playbook -i inventory deploy.yaml --ask-vault-pass
+
+# Use a password file
+ansible-playbook -i inventory deploy.yaml --vault-password-file ~/.vault_pass
+```
+
+### Limitation: Freeform Configurations
+
+Ansible Vault encrypts the entire value of a YAML field. This works for standalone fields like `authentication_key` where the complete value is a secret.
+
+However, freeform configuration blocks may contain a mix of regular configuration and secrets within a single multi-line string:
+
+```yaml
+# Does not work with Ansible Vault because only the TACACS key is a secret,
+# not the entire block.
+aaa_freeform: |
+  feature tacacs+
+  tacacs-server key 7 MySecretTacacsKey
+  ip tacacs source-interface mgmt0
+  tacacs-server timeout 20
+```
+
+Encrypting the entire `aaa_freeform` value with Ansible Vault would encrypt all four lines, which is not desired.
+
+---
+
+## Environment Variable Lookup (`env_var_`)
+
+The `env_var_` prefix instructs NaC to resolve a value from an environment variable at runtime. This works for:
+
+- **Standalone values** - the entire YAML value is an reference to an environment variable
+- **Embedded secrets** - `env_var_` references inside larger strings (e.g. freeform configuration blocks)
+
+### How It Works
+
+Any string value in the data model that contains `env_var_` is resolved by the NaC VXLAN `validate` role. The secret is replaced with the value of the corresponding environment variable.
+
+* Variable names in YAML must exactly match the environment variable names (including the env_var_ prefix).
+* Valid environment variable names may include letters, digits, and underscores.
+* Use single quotes to prevent shell interpretation of special characters
+* If the environment variable is not set, a warning is displayed and the secret is left unchanged.
+
+### Setting Environment Variables
+
+```bash
+export env_var_BGP_AUTH_KEY='MyBgpP@$$w0rd'
+export env_var_MCAST_AUTH_KEY='mcast_secret_123'
+export env_var_TACACS_KEY='TacacsSecret!'
+export env_var_DCI_PASSWORD='DciP@ssword'
+```
+
+### Examples: Standalone Values
+
+```yaml
+vxlan:
+  underlay:
+    multicast:
+      ipv4:
+        authentication_enable: true
+        authentication_key: env_var_MCAST_AUTH_KEY
+    bgp:
+      authentication_enable: true
+      authentication_key_type: 3
+      authentication_key: env_var_BGP_AUTH_KEY
+```
+
+```yaml
+vxlan:
+  multisite:
+    overlay_dci:
+      enable_ebgp_password: True
+      ebgp_password: env_var_DCI_PASSWORD
+      ebgp_password_encryption_type: 3
+```
+
+### Example: Freeform Configurations
+
+```yaml
+vxlan:
+  global:
+    ebgp:
+      aaa_freeform: |
+        feature tacacs+
+        tacacs-server key 7 env_var_TACACS_KEY
+        ip tacacs source-interface mgmt0
+        tacacs-server timeout 20
+```
+
+At runtime, only `env_var_TACACS_KEY` is replaced with the value of the `env_var_TACACS_KEY` environment variable. The rest of the block is unchanged:
+
+```
+feature tacacs+
+tacacs-server key 7 TacacsSecret!
+ip tacacs source-interface mgmt0
+tacacs-server timeout 20
+```
+
+This pattern works in any freeform field (`aaa_freeform`, `banner_freeform`, `bootstrap_freeform`, `intra_fabric_link_freeform`, `freeform_config`, etc.) and supports multiple `env_var_` tokens in the same block.

plugins/action/common/prepare_plugins/prep_005_resolve_env_vars.py

@@ -0,0 +1,106 @@
+# Copyright (c) 2025 Cisco Systems, Inc. and its affiliates
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy of
+# this software and associated documentation files (the "Software"), to deal in
+# the Software without restriction, including without limitation the rights to
+# use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+# the Software, and to permit persons to whom the Software is furnished to do so,
+# subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+# FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+# COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+# IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+#
+# SPDX-License-Identifier: MIT
+
+import os
+import re
+from ansible.utils.display import Display
+
+display = Display()
+
+ENV_VAR_PREFIX = 'env_var_'
+
+# Matches env_var_ followed by one or more word characters (a-z, A-Z, 0-9, _)
+ENV_VAR_PATTERN = re.compile(r'env_var_\w+')
+
+
+def resolve_env_var_token(token, path):
+    """
+    Resolve a single env_var_ token to its environment variable value.
+
+    Note: Environment variables containing special characters like $, `, \\, etc.
+    should be properly escaped when setting them in the shell.
+    Example: export BGP_AUTH_KEY='MyP@$$w0rd' (use single quotes to prevent shell interpretation)
+    """
+    resolved = os.getenv(token)
+
+    if resolved is None:
+        display.warning(
+            f"Environment variable '{token}' referenced at "
+            f"'{path}' is not set. The value will not be resolved."
+        )
+        return token
+
+    display.vvv(f"Resolved '{token}' from environment variable at '{path}'")
+    return resolved
+
+
+def resolve_env_vars_in_string(value, path):
+    resolved_count = 0
+
+    def replace_match(match):
+        nonlocal resolved_count
+        token = match.group(0)
+        replacement = resolve_env_var_token(token, path)
+        if replacement != token:
+            resolved_count += 1
+        return replacement
+
+    new_value = ENV_VAR_PATTERN.sub(replace_match, value)
+    return new_value, resolved_count
+
+
+def resolve_env_vars_recursive(data, path=''):
+    resolved_count = 0
+
+    if isinstance(data, dict):
+        for key, value in data.items():
+            current_path = f"{path}.{key}" if path else key
+            if isinstance(value, str) and ENV_VAR_PREFIX in value:
+                data[key], count = resolve_env_vars_in_string(value, current_path)
+                resolved_count += count
+            elif isinstance(value, (dict, list)):
+                resolved_count += resolve_env_vars_recursive(value, current_path)
+    elif isinstance(data, list):
+        for index, item in enumerate(data):
+            current_path = f"{path}[{index}]"
+            if isinstance(item, str) and ENV_VAR_PREFIX in item:
+                data[index], count = resolve_env_vars_in_string(item, current_path)
+                resolved_count += count
+            elif isinstance(item, (dict, list)):
+                resolved_count += resolve_env_vars_recursive(item, current_path)
+
+    return resolved_count
+
+
+class PreparePlugin:
+    def __init__(self, **kwargs):
+        self.kwargs = kwargs
+        self.keys = []
+
+    def prepare(self):
+        data_model = self.kwargs['results']['model_extended']
+
+        resolved_count = resolve_env_vars_recursive(data_model)
+        if resolved_count > 0:
+            display.v(f"Resolved {resolved_count} environment variable(s) in the data model")
+
+        self.kwargs['results']['model_extended'] = data_model
+        return self.kwargs['results']