The 'payto' URI scheme for payments

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Table of Contents

1. Introduction

This document defines the 'payto' Uniform Resource Identifier (URI) [RFC3986] scheme for designating transfer form data for payments.¶

2. Syntax of a 'payto' URI

This document uses the Augmented Backus-Naur Form (ABNF) of [RFC5234].¶

  payto-URI = "payto://" authority path-abempty [ "?" opts ]
  opts = opt *( "&" opt )
  opt = (generic-opt / authority-specific-opt) "=" *pchar
  generic-opt = "amount" / "receiver-name" / "sender-name" /
                "message" / "instruction"
  authority-specific-opt = ALPHA *( ALPHA / DIGIT / "-" / "." )
  authority = ALPHA *( ALPHA / DIGIT / "-" / "." )

'path-abempty' is defined in [RFC3986] in Section 3.3. 'pchar' is defined in [RFC3986], Appendix A.¶

3. Semantics

The authority component of a payment URI identifies the payment target type. The payment target types are defined in the "Payment Target Types" sub-registry, see Section 10. The path component of the URI identifies the target for a payment as interpreted by the respective payment target type. The query component of the URI can provide additional parameters for a payment. Every payment target type SHOULD accept the options defined in generic-opt. The default operation of applications that invoke a URI with the payto scheme MUST be to launch an application (if available) associated with the payment target type that can initiate a payment. If multiple handlers are registered for the same payment target type, the user SHOULD be able to choose which application to launch. This allows users with multiple bank accounts (each accessed the respective bank's banking application) to choose which account to pay with. An application SHOULD allow dereferencing a payto URI even if the payment target type of that URI is not registered in the "Payment Target Types" sub-registry. Details of the payment MUST be taken from the path and options given in the URI. The user SHOULD be allowed to modify these details before confirming a payment.¶

4. Examples

  payto://iban/DE75512108001245126199?amount=EUR:200.0&message=hello

  INVALID (authority missing):  payto:iban/12345

5. Generic Options

Applications MUST accept URIs with options in any order. The "amount" option MUST NOT occur more than once. Other options MAY be allowed multiple times, with further restrictions depending on the payment target type. The following options SHOULD be understood by every payment target type.¶

amount: The amount to transfer. The format MUST be:¶

  amount = currency ":" unit [ "." fraction ]
  currency = 1*ALPHA
  unit = 1*(DIGIT / ",")
  fraction = 1*(DIGIT / ",")

If a 3-letter 'currency' is used, it MUST be an [ISO4217] alphabetic code. A payment target type MAY define semantics beyond ISO 4217 for currency codes that are not 3 characters. The 'unit' value MUST be smaller than 2^53. If present, the 'fraction' MUST consist of no more than 8 decimal digits. The use of commas is optional for readability and they MUST be ignored.¶

receiver-name: Name of the entity that receives the payment (creditor).¶

sender-name: Name of the entity that makes the payment (debtor).¶

message: A short message to identify the purpose of the payment, which MAY be subject to lossy conversions (for example, due to character set encoding limitations).¶

instruction: A short message giving instructions to the recipient, which MUST NOT be subject to lossy conversions. Character set limitations allowed for such instructions depend on the payment target type.¶

6. Internationalization and Character Encoding

Various payment systems use restricted character sets. An application that processes 'payto' URIs MUST convert characters that are not allowed by the respective payment systems into allowable character using either an encoding or a replacement table. This conversion process MAY be lossy, except for the instruction field.¶

To avoid special encoding rules for the payment target identifier, the userinfo component [RFC3986] is disallowed in payto URIs. Instead, the payment target identifier is given as an option, where encoding rules are uniform for all options.¶

7. Tracking Payment Target Types

A registry of Payment Target Types is described in Section 10. The registration policy for this registry is "First Come First Served", as described in [RFC8126]. When requesting new entries, careful consideration of the following criteria is strongly advised:¶

1. The description clearly defines the syntax and semantics of the payment target and optional parameters if applicable.¶
2. Relevant references are provided if they are available.¶
3. The chosen name is appropriate for the payment target type, does not conflict with well-known payment systems, and avoids potential to confuse users.¶
4. The payment system underlying the payment target type is not fundamentally incompatible with the general options (such as positive decimal amounts) in this specification.¶
5. The payment target type is not a vendor-specific version of a payment target type that could be described more generally by a vendor-neutral payment target type.¶
6. The specification of the new payment target type remains within the scope of payment transfer form data. In particular specifying complete invoices is not in scope. Neither are processing instructions to the payment processor or bank beyond a simple payment.¶
7. The payment target and the options do not contain the payment sender's account details.¶

Documents that support requests for new registry entries should provide the following information for each entry:¶

• Name: The name of the payment target type (case insensitive ASCII string, restricted to alphanumeric characters, dots and dashes)¶
• Description: A description of the payment target type, including the semantics of the path in the URI if applicable.¶
• Example: At least one example URI to illustrate the payment target type.¶
• Contact: The contact information of a person to contact for further information¶
• References: Optionally, references describing the payment target type (such as an RFC) and target-specific options, or references describing the payment system underlying the payment target type.¶

This document populates the registry with six entries as follows (see also Section 10).¶

8. Security Considerations

Interactive applications handling the payto URI scheme MUST NOT initiate any financial transactions without prior review and confirmation from the user, and MUST take measures to prevent clickjacking [HMW12].¶

Unless a payto URI is received over a trusted, authenticated channel, a user might not be able to identify the target of a payment. In particular due to homographs [unicode-tr36], a payment target type SHOULD NOT use human-readable names in combination with unicode in the target account specification, as it could give the user the illusion of being able to identify the target account from the URI.¶

To avoid unnecessary data collection, payment target types SHOULD NOT include personally identifying information about the sender of a payment that is not essential for an application to conduct a payment.¶

9. IANA Considerations

IANA maintains a registry called the "Uniform Resource Identifier (URI) Schemes" registry.¶

10. Payment Target Types

This document specifies a list of Payment Target Types. It is possible that future work will need to specify additional payment target types. The GNUnet Assigned Numbers Authority (GANA) [GANA] operates the "payto-payment-target-types" registry to track the following information for each payment target type:¶

• Name: The name of the payment target type (case insensitive ASCII string, restricted to alphanumeric characters, dots and dashes)¶
• Contact: The contact information of a person to contact for further information¶
• References: Optionally, references describing the payment target type (such as an RFC) and target-specific options, or references describing the payment system underlying the payment target type.¶

The entries that have been made for the "payto-payment-target-types" defined in this document are as follows:¶

    Name      | Contact                 | Reference
    ----------+-------------------------+------------
    ach       | N/A                     | [This.I-D]
    bic       | N/A                     | [This.I-D]
    iban      | N/A                     | [This.I-D]
    upi       | N/A                     | [This.I-D]
    bitcoin   | N/A                     | [This.I-D]
    ilp       | N/A                     | [This.I-D]
    void      | N/A                     | [This.I-D]

Authors' Addresses