diff --git a/samples/go/pkg/ap2/types/mandate.go b/samples/go/pkg/ap2/types/mandate.go
index 4aa6701c..6cfab83e 100644
--- a/samples/go/pkg/ap2/types/mandate.go
+++ b/samples/go/pkg/ap2/types/mandate.go
@@ -29,6 +29,7 @@ type IntentMandate struct {
 	SKUs                         []string `json:"skus,omitempty"`
 	RequiresRefundability        *bool    `json:"requires_refundability,omitempty"`
 	IntentExpiry                 string   `json:"intent_expiry"`
+	UserAuthorization            *string  `json:"user_authorization,omitempty"`
 }
 
 func NewIntentMandate() *IntentMandate {
@@ -75,6 +76,8 @@ type PaymentMandateContents struct {
 	PaymentDetailsTotal PaymentItem     `json:"payment_details_total"`
 	PaymentResponse     PaymentResponse `json:"payment_response"`
 	MerchantAgent       string          `json:"merchant_agent"`
+	IntentMandateID     *string         `json:"intent_mandate_id,omitempty"`
+	TransactionModality *string         `json:"transaction_modality,omitempty"`
 	Timestamp           string          `json:"timestamp,omitempty"`
 }
 
diff --git a/samples/python/src/roles/shopping_agent/tools.py b/samples/python/src/roles/shopping_agent/tools.py
index 1d8b7bf1..139aa7a4 100644
--- a/samples/python/src/roles/shopping_agent/tools.py
+++ b/samples/python/src/roles/shopping_agent/tools.py
@@ -31,6 +31,7 @@
 from ap2.types.contact_picker import ContactAddress
 from ap2.types.mandate import CART_MANDATE_DATA_KEY
 from ap2.types.mandate import CartMandate
+from ap2.types.mandate import IntentMandate
 from ap2.types.mandate import PAYMENT_MANDATE_DATA_KEY
 from ap2.types.mandate import PaymentMandate
 from ap2.types.mandate import PaymentMandateContents
@@ -240,6 +241,9 @@ def sign_mandates_on_user_device(tool_context: ToolContext) -> str:
   """
   payment_mandate: PaymentMandate = tool_context.state["payment_mandate"]
   cart_mandate: CartMandate = tool_context.state["cart_mandate"]
+  intent_mandate: IntentMandate | None = tool_context.state.get(
+      "intent_mandate"
+  )
   cart_mandate_hash = _generate_cart_mandate_hash(cart_mandate)
   payment_mandate_hash = _generate_payment_mandate_hash(
       payment_mandate.payment_mandate_contents
@@ -247,9 +251,15 @@ def sign_mandates_on_user_device(tool_context: ToolContext) -> str:
   # A JWT containing the user's digital signature to authorize the transaction.
   # The payload uses hashes to bind the signature to the specific cart and
   # payment details, and includes a nonce to prevent replay attacks.
-  payment_mandate.user_authorization = (
-      cart_mandate_hash + "_" + payment_mandate_hash
-  )
+  hashes = [cart_mandate_hash, payment_mandate_hash]
+
+  # In Human Not Present scenarios, include the intent mandate hash to bind
+  # the payment authorization to the user-signed intent mandate.
+  if intent_mandate:
+    intent_mandate_hash = _generate_intent_mandate_hash(intent_mandate)
+    hashes.append(intent_mandate_hash)
+
+  payment_mandate.user_authorization = "_".join(hashes)
   tool_context.state["signed_payment_mandate"] = payment_mandate
   return payment_mandate.user_authorization
 
@@ -302,6 +312,29 @@ def _generate_cart_mandate_hash(cart_mandate: CartMandate) -> str:
   return "fake_cart_mandate_hash_" + cart_mandate.contents.id
 
 
+def _generate_intent_mandate_hash(intent_mandate: IntentMandate) -> str:
+  """Generates a cryptographic hash of the IntentMandate.
+
+  This hash binds the user's payment authorization to the specific
+  user-signed Intent Mandate, ensuring that Human Not Present transactions
+  can be traced back to a verified user intent.
+
+  Note: This is a placeholder implementation for development. A real
+  implementation must use a secure hashing algorithm (e.g., SHA-256) on the
+  canonical representation of the IntentMandate object.
+
+  Args:
+      intent_mandate: The IntentMandate object to hash.
+
+  Returns:
+      A string representing the hash of the intent mandate.
+  """
+  return (
+      "fake_intent_mandate_hash_"
+      + intent_mandate.natural_language_description[:20]
+  )
+
+
 def _generate_payment_mandate_hash(
     payment_mandate_contents: PaymentMandateContents,
 ) -> str:
diff --git a/src/ap2/types/mandate.py b/src/ap2/types/mandate.py
index c5506689..42f653b8 100644
--- a/src/ap2/types/mandate.py
+++ b/src/ap2/types/mandate.py
@@ -74,6 +74,25 @@ class IntentMandate(BaseModel):
       ...,
       description="When the intent mandate expires, in ISO 8601 format.",
   )
+  user_authorization: Optional[str] = Field(
+      None,
+      description=(
+          """
+          A base64url-encoded JSON Web Token (JWT) that digitally signs the
+          intent mandate contents by the user's private key. This provides
+          non-repudiable proof of the user's intent and prevents tampering
+          by the shopping agent.
+
+          If this field is present, user_cart_confirmation_required can be
+          set to false, allowing the agent to execute purchases in the
+          user's absence.
+
+          If this field is None, user_cart_confirmation_required must be true,
+          requiring the user to confirm each specific purchase.
+          """
+      ),
+      example="eyJhbGciOiJFUzI1NksiLCJraWQiOiJkaWQ6ZXhhbXBsZ...",
+  )
 
 
 class CartContents(BaseModel):
@@ -154,6 +173,24 @@ class PaymentMandateContents(BaseModel):
       ),
   )
   merchant_agent: str = Field(..., description="Identifier for the merchant.")
+  intent_mandate_id: Optional[str] = Field(
+      None,
+      description=(
+          "Reference to the user-signed Intent Mandate that authorizes "
+          "this transaction in Human Not Present scenarios. This allows "
+          "the payment network to verify that the 'human not present' "
+          "transaction has pre-authorization support from a 'human present' "
+          "intent mandate. Required for HNP transactions."
+      ),
+  )
+  transaction_modality: Optional[str] = Field(
+      None,
+      description=(
+          "Transaction modality: 'human_present' or 'human_not_present'. "
+          "This signals to the payment network whether the user was present "
+          "at the time of payment authorization."
+      ),
+  )
   timestamp: str = Field(
       description=(
           "The date and time the mandate was created, in ISO 8601 format."