Support authentication using a JSON web token (JWT) #93

bless/aws_lambda/bless_lambda_user.py

@@ -17,6 +17,13 @@
     KMSAUTH_REMOTE_USERNAMES_ALLOWED_OPTION, \
     VALIDATE_REMOTE_USERNAMES_AGAINST_IAM_GROUPS_OPTION, \
     KMSAUTH_SERVICE_ID_OPTION, \
+    JWTAUTH_SECTION, \
+    JWTAUTH_USEJWTAUTH_OPTION, \
+    JWTAUTH_SIGNATURE_JWK_OPTION, \
+    JWTAUTH_AUDIENCE_OPTION, \
+    JWTAUTH_ISSUER_OPTION, \
+    JWTAUTH_SIGNATURE_ALGORITHM_OPTION, \
+    JWTAUTH_USERNAME_CLAIM_OPTION, \
     TEST_USER_OPTION, \
     CERTIFICATE_EXTENSIONS_OPTION, \
     REMOTE_USERNAMES_VALIDATION_OPTION, \
@@ -29,6 +36,8 @@
 from bless.ssh.certificates.ssh_certificate_builder_factory import get_ssh_certificate_builder
 from kmsauth import KMSTokenValidator, TokenValidationError
 from marshmallow.exceptions import ValidationError
+from jose import jwt
+from jose.exceptions import JWTError
 
 
 def lambda_handler_user(
@@ -159,6 +168,34 @@ def lambda_handler_user(
         else:
             return error_response('InputValidationError', 'Invalid request, missing kmsauth token')
 
+    # Authenticate the user with JWT, if key is configured
+    if config.getboolean(JWTAUTH_SECTION, JWTAUTH_USEJWTAUTH_OPTION):
+        if request.jwtauth_token:
+
+            if request.remote_usernames != request.bastion_user:
+                return error_response('JWTAuthValidationError',
+                                      'remote_usernames must be the same as bastion_user')
+            try:
+                claims = jwt.decode(
+                    request.jwtauth_token,
+                    config.get(JWTAUTH_SECTION, JWTAUTH_SIGNATURE_JWK_OPTION),
+                    audience=config.get(JWTAUTH_SECTION, JWTAUTH_AUDIENCE_OPTION),
+                    issuer=config.get(JWTAUTH_SECTION, JWTAUTH_ISSUER_OPTION),
+                    algorithms=config.get(JWTAUTH_SECTION, JWTAUTH_SIGNATURE_ALGORITHM_OPTION),
+                    options={'verify_at_hash': False}
+                )
+                username_claim = config.get(JWTAUTH_SECTION, JWTAUTH_USERNAME_CLAIM_OPTION)
+                if username_claim not in claims.keys():
+                    return error_response('JWTAuthValidationError',
+                                          'missing {} claim in jwt'.format(username_claim))
+                if request.bastion_user != claims[username_claim]:
+                    return error_response('JWTAuthValidationError',
+                                          'bastion_user must equal {} claim in jwt'.format(username_claim))
+            except JWTError as e:
+                return error_response('JWTAuthValidationError', str(e))
+        else:
+            return error_response('InputValidationError', 'Invalid request, missing jwtauth_token')
+
     # Build the cert
     ca = get_ssh_certificate_authority(ca_private_key, ca_private_key_password)
     cert_builder = get_ssh_certificate_builder(ca, SSHCertificateType.USER,

bless/config/bless_config.py

@@ -63,6 +63,25 @@
 KMSAUTH_SERVICE_ID_OPTION = 'kmsauth_serviceid'
 KMSAUTH_SERVICE_ID_DEFAULT = None
 
+JWTAUTH_SECTION = 'JWT Auth'
+JWTAUTH_USEJWTAUTH_OPTION = 'use_jwtauth'
+JWTAUTH_USEJWTAUTH_DEFAULT = 'False'
+
+JWTAUTH_SIGNATURE_JWK_OPTION = 'jwtauth_signature_jwk'
+JWTAUTH_SIGNATURE_JWK_DEFAULT = ''
+
+JWTAUTH_SIGNATURE_ALGORITHM_OPTION = 'jwtauth_signature_algorithm'
+JWTAUTH_SIGNATURE_ALGORITHM_DEFAULT = 'RS256'
+
+JWTAUTH_ISSUER_OPTION = 'jwtauth_issuer'
+JWTAUTH_ISSUER_DEFAULT = ''
+
+JWTAUTH_AUDIENCE_OPTION = 'jwtauth_audience'
+JWTAUTH_AUDIENCE_DEFAULT = ''
+
+JWTAUTH_USERNAME_CLAIM_OPTION = 'jwtauth_username_claim'
+JWTAUTH_USERNAME_CLAIM_DEFAULT = 'email'
+
 USERNAME_VALIDATION_OPTION = 'username_validation'
 USERNAME_VALIDATION_DEFAULT = 'useradd'
 
@@ -102,6 +121,12 @@ def __init__(self, aws_region, config_file):
                     KMSAUTH_KEY_ID_OPTION: KMSAUTH_KEY_ID_DEFAULT,
                     KMSAUTH_REMOTE_USERNAMES_ALLOWED_OPTION: KMSAUTH_REMOTE_USERNAMES_ALLOWED_OPTION_DEFAULT,
                     KMSAUTH_USEKMSAUTH_OPTION: KMSAUTH_USEKMSAUTH_DEFAULT,
+                    JWTAUTH_USEJWTAUTH_OPTION: JWTAUTH_USEJWTAUTH_DEFAULT,
+                    JWTAUTH_SIGNATURE_JWK_OPTION: JWTAUTH_SIGNATURE_JWK_DEFAULT,
+                    JWTAUTH_SIGNATURE_ALGORITHM_OPTION: JWTAUTH_SIGNATURE_ALGORITHM_DEFAULT,
+                    JWTAUTH_ISSUER_OPTION: JWTAUTH_ISSUER_DEFAULT,
+                    JWTAUTH_AUDIENCE_OPTION: JWTAUTH_AUDIENCE_DEFAULT,
+                    JWTAUTH_USERNAME_CLAIM_OPTION: JWTAUTH_USERNAME_CLAIM_DEFAULT,
                     CERTIFICATE_EXTENSIONS_OPTION: CERTIFICATE_EXTENSIONS_DEFAULT,
                     USERNAME_VALIDATION_OPTION: USERNAME_VALIDATION_DEFAULT,
                     REMOTE_USERNAMES_VALIDATION_OPTION: REMOTE_USERNAMES_VALIDATION_DEFAULT,
@@ -125,6 +150,9 @@ def __init__(self, aws_region, config_file):
         if not self.has_section(KMSAUTH_SECTION):
             self.add_section(KMSAUTH_SECTION)
 
+        if not self.has_section(JWTAUTH_SECTION):
+            self.add_section(JWTAUTH_SECTION)
+
         if not self.has_option(BLESS_CA_SECTION, self.aws_region + REGION_PASSWORD_OPTION_SUFFIX):
             if not self.has_option(BLESS_CA_SECTION, 'default' + REGION_PASSWORD_OPTION_SUFFIX):
                 raise ValueError("No Region Specific And No Default Password Provided.")

bless/config/bless_deploy_example.cfg

@@ -63,3 +63,24 @@ ca_private_key_file = <INSERT_YOUR_ENCRYPTED_PEM_FILE_NAME>
 # the group name is "ssh-{}".format(remote_username), but that can be changed here. The groups must have a
 # consistent naming scheme and must all contain the remote_username once. For example, ssh-ubuntu.
 # kmsauth_iam_group_name_format = ssh-{}
+
+# This section is optional
+[JWT Auth]
+# Enable authentication via a JWT, to ensure a username matches a claim in a valid JWT
+# use_jwtauth = True
+
+# The JWK containing the public key used to verify the JWT signature, in JSON Web Key format https://tools.ietf.org/html/rfc7517
+# jwtauth_signature_jwk = {"kty": "RSA","e": "...","use": "sig","kid": "...","alg": "RS256","n": "..."}
+
+# The expected signature algorithm. JWTs signed with a different algorithm will be rejected.
+# jwtauth_signature_algorithm = RS256
+
+# The issuer present as the iss claim in the JWT. This must match the issuer from your identity provider.
+# jwtauth_issuer = https://accounts.google.com
+
+# The audience present as the aud claim in the JWT. This must match the audience from your identity provider.
+# jwtauth_audience = 1234567890-1234567890abcd.apps.googleusercontent.com
+
+# The claim in the JWT that contains the username. This is compared to the requested username, and will be set in the
+# principals list of the SSH certificate.
+# jwtauth_username_claim = email

bless/request/bless_request_user.py

@@ -90,6 +90,7 @@ class BlessUserSchema(Schema):
     public_key_to_sign = fields.Str(validate=validate_ssh_public_key, required=True)
     remote_usernames = fields.Str(required=True)
     kmsauth_token = fields.Str(required=False)
+    jwtauth_token = fields.Str(required=False)
 
     @validates_schema(pass_original=True)
     def check_unknown_fields(self, data, original_data):
@@ -125,7 +126,7 @@ def validate_remote_usernames(self, remote_usernames):
 
 class BlessUserRequest:
     def __init__(self, bastion_ips, bastion_user, bastion_user_ip, command, public_key_to_sign,
-                 remote_usernames, kmsauth_token=None):
+                 remote_usernames, kmsauth_token=None, jwtauth_token=None):
         """
         A BlessRequest must have the following key value pairs to be valid.
         :param bastion_ips: The source IPs where the SSH connection will be initiated from.  This is
@@ -138,6 +139,7 @@ def __init__(self, bastion_ips, bastion_user, bastion_user_ip, command, public_k
         :param remote_usernames: Comma-separated list of username(s) or authorized principals on the remote
         server that will be used in the SSH request.  This is enforced in the issued certificate.
         :param kmsauth_token: An optional kms auth token to authenticate the user.
+        :param jwtauth_token: An optional jwt token to authenticate the user.
         """
         self.bastion_ips = bastion_ips
         self.bastion_user = bastion_user
@@ -146,6 +148,7 @@ def __init__(self, bastion_ips, bastion_user, bastion_user_ip, command, public_k
         self.public_key_to_sign = public_key_to_sign
         self.remote_usernames = remote_usernames
         self.kmsauth_token = kmsauth_token
+        self.jwtauth_token = jwtauth_token
 
     def __eq__(self, other):
         return self.__dict__ == other.__dict__

requirements.txt

@@ -14,3 +14,4 @@ python-dateutil==2.8.0
 s3transfer==0.2.0
 six==1.12.0
 urllib3==1.24.3
+python-jose[cryptography]==3.0.1

setup.py

@@ -21,8 +21,9 @@
         'boto3',
         'cryptography',
         'ipaddress',
-        'marshmallow',
-        'kmsauth'
+        'marshmallow<3',
+        'kmsauth',
+        'python-jose[cryptography]'
     ],
     extras_require={
         'tests': [

tests/aws_lambda/bless-test-jwtauth.cfg

@@ -0,0 +1,12 @@
+[Bless CA]
+ca_private_key_file = tests/aws_lambda/only-use-for-unit-tests.pem
+us-east-1_password = bogus-password-for-unit-test
+us-west-2_password = bogus-password-for-unit-test
+
+[JWT Auth]
+use_jwtauth = True
+jwtauth_signature_jwk = {"kty": "RSA","e": "AQAB","use": "sig","kid": "key1","alg": "RS256","n": "7V4O45XkdzKedgfbg3U1X_UeGF00wQH6APcuRX_702h-3QZI4VmAbBFgDDAJgHa1wunKPUKmwfmzFodLX6Bd2UvgHtzhHDAnrHYSOpV0jci7zxUhPN84PBbNRKNG-yAGPvNk4YbCWHywz7BKmTVnG9q4KSdWaHpyhljxedMdkt2JqdTJcwaAEfqT_0A-gcBWxyCPwRJJRLColM9g6lZU7-17Y3UNHwBFC4lahfd009CXY7WMbKIJMG0LuBjsmCE4L__IlrFlevVFyA0ShDjDh07gKD-f5WJ6WdgcZOL7X3rf-DK6MRBUW4ItIpG7DVVWN0Vj6SNQT3x1kwq55mIZTw"}
+jwtauth_signature_algorithm = RS256
+jwtauth_issuer = https://issuer.example.com
+jwtauth_audience = 6c1d8893-9240-4f87-be95-1f21ef664ce0
+jwtauth_username_claim = username