Add DLP code sample and test for de-id free text with surrogate (GoogleCloudPlatform#4085)

## Description
Add DLP code sample and test for de-id free text with surrogate, meant for https://cloud.google.com/dlp/docs/pseudonymization#de-identification_in_free_text_code_example

## Checklist
- [x] I have followed [Sample Guidelines from AUTHORING_GUIDE.MD](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md)
- [ ] README is updated to include [all relevant information](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#readme-file)
- [x] **Tests** pass:   `nox -s py-3.6` (see [Test Enviroment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#test-environment-setup))
- [x] **Lint** pass:   `nox -s lint` (see [Test Enviroment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#test-environment-setup))
- [ ] These samples need a new **API enabled** in testing projects to pass (let us know which ones)
- [ ] These samples need a new/updated **env vars** in testing projects set to pass (let us know which ones)
- [x] Please **merge** this PR for me once it is approved.

Author: lxhfirenking

dlp/deid.py

@@ -394,6 +394,93 @@ def reidentify_with_fpe(
 
 # [END dlp_reidentify_fpe]
 
+
+# [START dlp_deidentify_free_text_with_fpe_using_surrogate]
+def deidentify_free_text_with_fpe_using_surrogate(
+    project,
+    input_str,
+    alphabet="NUMERIC",
+    info_type="PHONE_NUMBER",
+    surrogate_type="PHONE_TOKEN",
+    unwrapped_key="YWJjZGVmZ2hpamtsbW5vcA==",
+):
+    """Uses the Data Loss Prevention API to deidentify sensitive data in a
+       string using Format Preserving Encryption (FPE).
+       The encryption is performed with an unwrapped key.
+    Args:
+        project: The Google Cloud project id to use as a parent resource.
+        input_str: The string to deidentify (will be treated as text).
+        alphabet: The set of characters to replace sensitive ones with. For
+            more information, see https://cloud.google.com/dlp/docs/reference/
+            rest/v2beta2/organizations.deidentifyTemplates#ffxcommonnativealphabet
+        info_type: The name of the info type to de-identify
+        surrogate_type: The name of the surrogate custom info type to use. Can
+            be essentially any arbitrary string, as long as it doesn't appear
+            in your dataset otherwise.
+        unwrapped_key: The base64-encoded AES-256 key to use.
+    Returns:
+        None; the response from the API is printed to the terminal.
+    """
+    # Import the client library
+    import google.cloud.dlp
+
+    # Instantiate a client
+    dlp = google.cloud.dlp_v2.DlpServiceClient()
+
+    # Convert the project id into a full resource id.
+    parent = dlp.project_path(project)
+
+    # The unwrapped key is base64-encoded, but the library expects a binary
+    # string, so decode it here.
+    import base64
+
+    unwrapped_key = base64.b64decode(unwrapped_key)
+
+    # Construct de-identify config
+    transformation = {
+        "info_types": [{"name": info_type}],
+        "primitive_transformation": {
+            "crypto_replace_ffx_fpe_config": {
+                "crypto_key": {
+                    "unwrapped": {"key": unwrapped_key}
+                },
+                "common_alphabet": alphabet,
+                "surrogate_info_type": {"name": surrogate_type},
+            }
+        }
+    }
+
+    deidentify_config = {
+        "info_type_transformations": {
+            "transformations": [transformation]
+        }
+    }
+
+    # Construct the inspect config, trying to finding all PII with likelihood
+    # higher than UNLIKELY
+    inspect_config = {
+        "info_types": [{"name": info_type}],
+        "min_likelihood": "UNLIKELY"
+    }
+
+    # Convert string to item
+    item = {"value": input_str}
+
+    # Call the API
+    response = dlp.deidentify_content(
+        parent,
+        inspect_config=inspect_config,
+        deidentify_config=deidentify_config,
+        item=item,
+    )
+
+    # Print results
+    print(response.item.value)
+
+
+# [END dlp_deidentify_free_text_with_fpe_using_surrogate]
+
+
 # [START dlp_reidentify_free_text_with_fpe_using_surrogate]
 def reidentify_free_text_with_fpe_using_surrogate(
     project,

dlp/deid_test.py

@@ -206,6 +206,25 @@ def test_reidentify_with_fpe(capsys):
     assert "731997681" not in out
 
 
+def test_deidentify_free_text_with_fpe_using_surrogate(capsys):
+    labeled_fpe_string = "My phone number is 4359916732"
+
+    deid.deidentify_free_text_with_fpe_using_surrogate(
+        GCLOUD_PROJECT,
+        labeled_fpe_string,
+        info_type="PHONE_NUMBER",
+        surrogate_type="PHONE_TOKEN",
+        unwrapped_key=UNWRAPPED_KEY,
+        alphabet="NUMERIC",
+    )
+
+    out, _ = capsys.readouterr()
+
+    assert "PHONE_TOKEN" in out
+    assert "My phone number is" in out
+    assert "4359916732" not in out
+
+
 def test_reidentify_free_text_with_fpe_using_surrogate(capsys):
     labeled_fpe_string = "My phone number is PHONE_TOKEN(10):9617256398"