diff --git a/src/awsrun/config.py b/src/awsrun/config.py
index 83870c7..d26e479 100644
--- a/src/awsrun/config.py
+++ b/src/awsrun/config.py
@@ -338,7 +338,7 @@ def __init__(self, type_):
         self.type = type_
 
     def type_check(self, obj):
-        return type(obj) == self.type
+        return type(obj) == self.type  # noqa: E721
 
     def __str__(self):
         return self.type.__name__
@@ -354,7 +354,7 @@ def __init__(self, pattern):
         self.pattern = pattern
 
     def type_check(self, obj):
-        if type(obj) != str:
+        if type(obj) != str:  # noqa: E721
             return False
         return bool(re.search(self.pattern, obj))
 
@@ -366,7 +366,7 @@ class IpAddress(Type):
     """Represents a string matching an IP address (v4 or v6)."""
 
     def type_check(self, obj):
-        if type(obj) != str:
+        if type(obj) != str:  # noqa: E721
             return False
         try:
             ipaddress.ip_address(obj)
@@ -382,7 +382,7 @@ class IpNetwork(Type):
     """Represents a string matching an IP network (v4 or v6)."""
 
     def type_check(self, obj):
-        if type(obj) != str:
+        if type(obj) != str:  # noqa: E721
             return False
         try:
             ipaddress.ip_network(obj)
@@ -398,7 +398,7 @@ class FileType(Type):
     """Represents a string pointing to an existing file."""
 
     def type_check(self, obj):
-        if type(obj) != str:
+        if type(obj) != str:  # noqa: E721
             return False
         return Path(obj).exists()
 
@@ -462,7 +462,7 @@ def __init__(self, element_type):
         self.element_type = element_type
 
     def type_check(self, obj):
-        if type(obj) != list:
+        if type(obj) != list:  # noqa: E721
             return False
         return all(self.element_type.type_check(e) for e in obj)
 
@@ -485,7 +485,7 @@ def __init__(self, key_type, value_type):
         self.value_type = value_type
 
     def type_check(self, obj):
-        if type(obj) != dict:
+        if type(obj) != dict:  # noqa: E721
             return False
         return all(self.key_type.type_check(k) for k in obj.keys()) and all(
             self.value_type.type_check(v) for v in obj.values()
diff --git a/src/awsrun/plugins/creds/aws.py b/src/awsrun/plugins/creds/aws.py
index bb0a0a2..4a01adf 100644
--- a/src/awsrun/plugins/creds/aws.py
+++ b/src/awsrun/plugins/creds/aws.py
@@ -137,6 +137,7 @@ class SAML(Plugin):
             role: STRING*
             url: STRING*
             auth_type: ("basic" | "digest" | "ntlm")
+            http_method: ("GET"| "POST")
             http_headers:
               STRING: STRING
             no_verify: BOOLEAN
@@ -175,6 +176,11 @@ class SAML(Plugin):
     specified, it must be one of `basic`, `digest`, or `ntlm`. The default value
     is `basic`. If using NTLM, username should be specified as `domain\\username`.
 
+    `http_method`
+    : The HTTP method to use when authenticating with the IdP. If
+    specified, it must be one of `GET`, `POST`. The default value
+    is `GET`.
+
     `http_headers`
     : Additional HTTP headers to send in the request to the IdP. If specified,
     it must be a dictionary of `key: value` pairs, where keys and values are
@@ -275,6 +281,7 @@ def instantiate(self, args):
             role=args.saml_role,
             url=cfg("url", type=URL, must_exist=True),
             auth=auth(args.saml_username, args.saml_password),
+            http_method=cfg("http_method", type=Choice("GET", "POST"), default="GET"),
             headers=cfg("http_headers", type=Dict(Str, Str), default={}),
             duration=args.saml_duration,
             saml_duration=args.saml_assertion_duration,
@@ -458,6 +465,7 @@ class SAMLCrossAccount(AbstractCrossAccount):
             role: STRING*
             url: STRING*
             auth_type: ("basic" | "digest" | "ntlm")
+            http_method: ("GET"| "POST")
             http_headers:
               STRING: STRING
             no_verify: BOOLEAN
@@ -503,6 +511,11 @@ class SAMLCrossAccount(AbstractCrossAccount):
     specified, it must be one of `basic`, `digest`, or `ntlm`. The default value
     is `basic`. If using NTLM, username should be specified as `domain\\username`.
 
+    `http_method`
+    : The HTTP method to use when authenticating with the IdP. If
+    specified, it must be one of `GET`, `POST`. The default value
+    is `GET`.
+
     `http_headers`
     : Additional HTTP headers to send in the request to the IdP. If specified,
     it must be a dictionary of `key: value` pairs, where keys and values are
diff --git a/src/awsrun/session/aws.py b/src/awsrun/session/aws.py
index aff8bac..e1a19ca 100644
--- a/src/awsrun/session/aws.py
+++ b/src/awsrun/session/aws.py
@@ -384,6 +384,7 @@ def __init__(
         role,
         url,
         auth,
+        http_method,
         headers=None,
         duration=3600,
         saml_duration=300,
@@ -392,6 +393,7 @@ def __init__(
         super().__init__(role, duration)
         self._url = url
         self._auth = auth
+        self._http_method = http_method
         self._headers = {} if headers is None else headers
         self._cached_saml = ExpiringValue(self._request_assertion, saml_duration)
         self._no_verify = no_verify
@@ -414,7 +416,15 @@ def _request_assertion(self):
         with requests.Session() as s:
             s.auth = self._auth
             s.headers.update(self._headers)
-            resp = s.get(self._url, verify=not self._no_verify)
+            if self._http_method == "GET":
+                resp = s.get(self._url, verify=not self._no_verify)
+            else:
+                authData = {
+                    "UserName": s.auth.username,
+                    "Password": s.auth.password,
+                    "AuthMethod": "FormsAuthentication",
+                }
+                resp = s.post(self._url, data=authData, verify=not self._no_verify)
 
         if resp.status_code == 401:
             raise IDPAccessDeniedException("Could not authenticate")