[samprotas]

The number of comments here specifically upset with this part of the current design is a bit discouraging, but not necessarily surprising.

Yes, many mainstream languages have near-zero support for Tagged/Discriminated Unions or Enums with Associated Data or Algebraic Data Types (pick your favorite name for the same concept). This is a limitation of those languages, which should not force a language-agnostic protocol to adopt the lowest common denominator of expressiveness.

Consider the problem they're avoiding of mutually exclusive keys in a struct/object. What do you do if you receive more than one? Is that behavior undefined? If it is defined, how sure are you that the implementation your package manager installed for you doesn't just pick one key arbitrarily in the name of "developer friendliness" leading to security bugs? This seems like a much more bug-ridden problem to solve than having to write verbose type/switching golang/java.

Implementing more verbose deserialization code in languages with no support for Tagged Unions seems like a small price to pay for making a protocol that leaves no room for undefined behavior.

To be clear, _many_ statically typed languages have perfect support for this concept (Rust/Swift/Scala/Haskell, to name a few).

[parhamn]

> To be clear, _many_ statically typed languages have perfect support for this concept (Rust/Swift/Scala/Haskell, to name a few).

No they don't, at least in the way you're selling it. The "limitation" here is JSON which doesn't attach type information. You're going to have to implement some typing protocol on top of the JSON anyway which will face similar problems to the ones you raised (unless you do some trait based inference which could be ambiguous and dangerous).

If they were Enums/Unions over a serialization protocol like protobuf, maybe your case makes sense. Even then, Im guessing a large % of the OAuth 3 requests will go through Java/Golang libraries, so on a practical level this is a bad idea too.

[samprotas]

I agree that having multiple different types of "object values" share one JSON key with no explicit "type" tag is asking for trouble with extensibility and conflicts.

That said, I think the constructive suggestion would be: "add a type tag to all objects in a union" (something suggested elsewhere in this thread).

Their "handles" can still claim "just a string" to save bandwidth in the common case, arrays can still represent "many things" and objects require "type" to be dis-ambiguous.

Most of the comments below don't mention the (real and important, but easily solvable) issue you've brought up however. They primarily fall into one of two buckets:

- It's hard to work with data shaped like this in my language (ex: java/go)

- It's hard to deserialize data shaped like this into my language that has no tagged unions (ex: java/go)

My biggest counterpoint to all of these complaints is: The fact that your language of choice cannot represent the concept of "one of these things" doesn't change the fact that this accurately describes reality sometimes.

A protocol with mutually exclusive keys (or really anything) by convention is strictly more bug-prone than a protocol with an object that is correct by construction.

[oaiey]

A protocol which is cumbersome to implement in many languages. Hmmm what can't go wrong. Partial support, late support of extensions, bugs,...

IMHO: a very bad choice. Complicated basic and higher level elements of protocols are the death of them (remember SOAP). I follow the train of thoughts to not restrict yourself too much but if (eg) java or C++ cannot implement it easy, not a good idea.

[samprotas]

Protobuf supports "oneof" which is also cumbersome to implement in these same languages but all of them support it (with some extra LOC and no exhaustiveness checking watching your back).

Java/Go/C++ are perfectly capable of parsing a "type" key and conditionally parsing different shaped data. If you make a programming mistake here, you'll get a parse error (bad, but not a security problem). The pushback seems to be that a Java/Go/C++ implementation adds LOCS and won't gain much by doing this extra step so lets make the protocol itself match match their (less precise) data representation.

FWIW there is work towards improving Java in this regard: https://cr.openjdk.java.net/~briangoetz/amber/pattern-match....

[oaiey]

But is not that elementary OOP polymorphism? It all depends on the fact whether the type is annotated or whether it needs to be analyzed from the data by probing. And types annotation are present in protobuf parts I remember :).

[Touche]

> This is a limitation of those languages, which should not force a language-agnostic protocol to adopt the lowest common denominator of expressiveness.

It's an intentional decision made by those languages in order to focus on other things. If your intent is to be language-agnostic, then yeah, going with lowest common denominator concepts is exactly what you need to do. If you just want to write a Haskell auth implementation using your favorite pet language features, then write a Haskell auth implementation.

[GordonS]

It's not the same as union types, but you can also often achieve polymorphic serialisation with any OO language, through the use of interfaces.

[dgritsko]

My fingers are firmly crossed that DUs make their way into C# 10... https://github.com/dotnet/csharplang/blob/master/proposals/d...