utility function for getting user email from x509 certificate

atst/domain/authnid/utils.py

@@ -1,7 +1,9 @@
 import re
 
+import cryptography.x509 as x509
+from cryptography.hazmat.backends import default_backend
+
 
-# TODO: our sample SDN does not have an email address
 def parse_sdn(sdn):
     try:
         parts = sdn.split(",")
@@ -9,5 +11,21 @@ def parse_sdn(sdn):
         cn = cn_string.split("=")[-1]
         info = cn.split(".")
         return {"last_name": info[0], "first_name": info[1], "dod_id": info[-1]}
+
     except (IndexError, AttributeError):
         raise ValueError("'{}' is not a valid SDN".format(sdn))
+
+
+def email_from_certificate(cert_file):
+    cert = x509.load_pem_x509_certificate(cert_file, default_backend())
+    try:
+        ext = cert.extensions.get_extension_for_class(x509.SubjectAlternativeName)
+        email = ext.value.get_values_for_type(x509.RFC822Name)
+        if email:
+            return email[0]
+
+        else:
+            raise ValueError("No email available for certificate with serial {}".format(cert.serial_number))
+
+    except x509.extensions.ExtensionNotFound:
+        raise ValueError("No subjectAltName available for certificate with serial {}".format(cert.serial_number))

tests/domain/authnid/test_utils.py

@@ -5,12 +5,38 @@ from tests.mocks import DOD_SDN
 
 def test_parse_sdn():
     parsed = utils.parse_sdn(DOD_SDN)
-    assert parsed.get('first_name') == 'ART'
+    assert parsed.get("first_name") == "ART"
-    assert parsed.get('last_name') == 'GARFUNKEL'
+    assert parsed.get("last_name") == "GARFUNKEL"
-    assert parsed.get('dod_id') == '5892460358'
+    assert parsed.get("dod_id") == "5892460358"
+
 
 def test_parse_bad_sdn():
     with pytest.raises(ValueError):
-        utils.parse_sdn('this has nothing to do with anything')
+        utils.parse_sdn("this has nothing to do with anything")
     with pytest.raises(ValueError):
         utils.parse_sdn(None)
+
+
+FIXTURE_EMAIL_ADDRESS = "artgarfunkel@uso.mil"
+
+
+def test_parse_email_cert():
+    cert_file = open("tests/fixtures/{}.crt".format(FIXTURE_EMAIL_ADDRESS), "rb").read()
+    email = utils.email_from_certificate(cert_file)
+    assert email == FIXTURE_EMAIL_ADDRESS
+
+
+def test_parse_cert_with_no_email():
+    cert_file = open("tests/fixtures/no-email.crt", "rb").read()
+    with pytest.raises(ValueError) as excinfo:
+        email = utils.email_from_certificate(cert_file)
+    (message,) = excinfo.value.args
+    assert "email" in message
+
+
+def test_parse_cert_with_no_san():
+    cert_file = open("tests/fixtures/no-san.crt", "rb").read()
+    with pytest.raises(ValueError) as excinfo:
+        email = utils.email_from_certificate(cert_file)
+    (message,) = excinfo.value.args
+    assert "subjectAltName" in message

tests/fixtures/artgarfunkel@uso.mil.crt

@@ -0,0 +1,29 @@
+-----BEGIN CERTIFICATE-----
+MIIE8DCCAtigAwIBAgIJALTstfJQuulmMA0GCSqGSIb3DQEBCwUAMCUxIzAhBgNV
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+-----END CERTIFICATE-----

tests/fixtures/no-email.crt

@@ -0,0 +1,29 @@
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+-----END CERTIFICATE-----

tests/fixtures/no-san.crt

@@ -0,0 +1,31 @@
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+-----END CERTIFICATE-----