Preparation, Enforcement, and Comparison of Internationalized Strings Representing Usernames and Passwords

Uniform Resource Names (URNs)

“…To the extent feasible and consistent with the requirements of names defined and standardized elsewhere, as well as the principles discussed in Section 1.2, the characters used to represent names SHOULD be restricted to either ASCII letters and digits or to the characters and syntax of some widely used models such as those of Internationalizing Domain Names in Applications (IDNA) [RFC5890], Preparation, Enforcement, and Comparison of Internationalized Strings (PRECIS) [RFC7613], or the Unicode Identifier and Pattern Syntax specification [UAX31].…”

PRECIS Framework: Preparation, Enforcement, and Comparison of Internationalized Strings in Application Protocols

“…Whereas the string classes define the "baseline" code points for a range of applications, profiling enables application protocols to apply the string classes in ways that are appropriate for common constructs such as usernames [RFC8265], opaque strings such as passwords [RFC8265], and nicknames [RFC8266]. Profiles are responsible for defining the handling of right-to-left code points as well as various mapping operations of the kind also discussed for IDNs in [RFC5895], such as case preservation or lowercasing, Unicode normalization, mapping of certain code points to other code points or to nothing, and mapping of fullwidth and halfwidth code points.…”

“…Some application technologies need strings that can be used in a free-form way, e.g., as a password in an authentication exchange (see [RFC8265]) or a nickname in a chat room (see [RFC8266]). We group such things into a class called "FreeformClass" having the following features.…”

“…Examples for profiles of the FreeformClass can be found in [RFC8265] (the OpaqueString profile) and [RFC8266] (the Nickname profile).…”

“…Depending on the deployment, a simple username might take the form of a user's full name (e.g., the user's personal name followed by a space and then the user's family name). Such a simple username cannot be defined as an instance of the IdentifierClass or a profile thereof, because space code points are not allowed in the IdentifierClass; however, it could be defined using a space-separated sequence of IdentifierClass instances, as in the following ABNF [RFC5234] from [RFC8265]: username = userpart *(1*SP userpart) userpart = 1*(idpoint) ; ; an "idpoint" is a Unicode code point that ; can be contained in a string conforming to ; the PRECIS IdentifierClass ; Similar techniques could be used to define many application-layer constructs, say of the form "user@domain" or "/path/to/file".…”