Reopen 7439 - ModelState json serialization should be camel cased

Describe the bug

The issue 7439 was not completely addressed, the bot blocked the issue from commenting, but I think this main problem should be addressed:

As is, Net Core responds almost everything as camel case, except for model validations, which I think is odd:

{
  "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
  "title": "One or more validation errors occurred.",
  "status": 400,
  "traceId": "|706e0133-46db8fce16cb675d.",
  "errors": {
    "Email": [
      "The Email field is not a valid e-mail address."
    ],
    "Password": [
      "The field Password must be a string or array type with a minimum length of '8'."
    ]
  }
}

As you see, all the properties are camel case but the field names, a workaround is to use CustomProblemDetailsFactory from the comment in the same issue.

To Reproduce

Create a project and a controller with a model with validations.

Make sure the controller is annotated with [ApiController], so validation is handled automatically.

Example:

    [Authorize]
    [ApiController]
    [Route("Api/Address/[controller]")]
    public class ColonyController : Controller
    {
        
        [HttpPost]
        [Route("[action]")]
        public Task<int> Create([FromBody]ColonyToAddDto colonyToAddDto)
        {
            return Task.FromResult(0);
        }
    }

With the model

    public class ColonyToAddDto
    {
        [Required]
        [StringLength(300, MinimumLength = 3)]
        public string Name { get; set; }
        [Range(1, 99999)]
        public int PostalCode { get; set; }
        [Range(1, double.PositiveInfinity)]
        public int MunicipalityId { get; set; }
    }

Further technical details

• ASP.NET Core version 3.1

[antonioortizpola]

I do not agree with the labels applied to this issue, as @TanvirArjel says:

• This is a bug, not an enhancement
• This does not affect a few, it affects anyone with a SPA wanting to use validation with the JSON standard camel-case.
• It is not a nice a to have, it is a bug that breaks apps and the docs, and needs time and research to apply workarounds for something really, really basic

[bcronje]

@javiercn @pranavkm can I implore that you reconsider the affected-few and severity-nice-to-have labels and re-apply it as a bug? This issue is still present in .NET 5 and clearly does not honor the DictionaryKeyPolicy = JsonNamingPolicy.CamelCase policy. I think it is safe to say the majority of users consuming an API from javascript expects camelcase properties, so not sure why you would think it only affects a few?

See also the following two issues which has been closed by bot:

https://github.com/dotnet/aspnetcore/issues/7439 https://github.com/dotnet/runtime/issues/31849

How can the below “Email” and “Password” keys not be considered a bug?

{
  "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
  "title": "One or more validation errors occurred.",
  "status": 400,
  "traceId": "|706e0133-46db8fce16cb675d.",
  "errors": {
    "Email": [
      "The Email field is not a valid e-mail address."
    ],
    "Password": [
      "The field Password must be a string or array type with a minimum length of '8'."
    ]
  }
}