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fix: add user_authorization to IntentMandate and intent binding to PaymentMandate #189

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fix: add user_authorization to IntentMandate and intent binding to PaymentMandate #189

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3 changes: 3 additions & 0 deletions samples/go/pkg/ap2/types/mandate.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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 {
Expand Down Expand Up @@ -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"`
}

Expand Down
39 changes: 36 additions & 3 deletions samples/python/src/roles/shopping_agent/tools.py
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -240,16 +241,25 @@ 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
)
# 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

Expand Down Expand Up @@ -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:
Expand Down
37 changes: 37 additions & 0 deletions src/ap2/types/mandate.py
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Original file line number Diff line number Diff line change
Expand Up @@ -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...",
)
Comment on lines +77 to +95
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@gemini-code-assist gemini-code-assist bot Mar 18, 2026

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medium

The description for user_authorization states an important business rule: "If this field is None, user_cart_confirmation_required must be true". To ensure data integrity and prevent invalid model states, this rule should be enforced with a Pydantic validator.

Here is an example of how you could implement this with a model_validator:

from pydantic import model_validator

class IntentMandate(BaseModel):
    # ... existing fields ...

    @model_validator(mode='after')
    def check_user_authorization_logic(self) -> 'IntentMandate':
        if self.user_authorization is None and not self.user_cart_confirmation_required:
            raise ValueError(
                'user_cart_confirmation_required must be True if user_authorization is not provided'
            )
        return self

This will make your model more robust.



class CartContents(BaseModel):
Expand Down Expand Up @@ -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."
),
)
Comment on lines +176 to +185
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@gemini-code-assist gemini-code-assist bot Mar 18, 2026

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medium

The description for intent_mandate_id mentions it is "Required for HNP transactions." This is a critical validation rule that should be enforced within the model to maintain data consistency. You can use a Pydantic model_validator to ensure intent_mandate_id is provided when transaction_modality is set for a Human Not Present transaction.

Here's how you could implement this check:

from pydantic import model_validator

class PaymentMandateContents(BaseModel):
    # ... existing fields ...

    @model_validator(mode='after')
    def check_hnp_requirements(self) -> 'PaymentMandateContents':
        if self.transaction_modality == 'human_not_present' and self.intent_mandate_id is None:
            raise ValueError('intent_mandate_id is required for human_not_present transactions')
        return self

(Note: This example assumes transaction_modality is a string. If you adopt the Enum suggestion from another comment, you would compare against the enum member, e.g., TransactionModality.HUMAN_NOT_PRESENT.)

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."
),
)
Comment on lines +186 to +193
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medium

The transaction_modality field accepts a limited set of string values: 'human_present' or 'human_not_present'. Using a plain string is susceptible to errors from typos or case variations. It's a best practice to use an Enum for such fields to enforce valid values, which improves code clarity and robustness.

You could define an Enum and use it for this field:

from enum import Enum

class TransactionModality(str, Enum):
    HUMAN_PRESENT = "human_present"
    HUMAN_NOT_PRESENT = "human_not_present"

class PaymentMandateContents(BaseModel):
    # ...
    transaction_modality: Optional[TransactionModality] = Field(
        None,
        description=(
            "Transaction modality. 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."
Expand Down
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