https://github.com/sample-by-jsakamoto/Blazor-UseGoogleReCAPTCHA
is a sample implementation of reCaptcha V2 for Blazor. It contains a class named SampleApi which in turn contains the following line that fails to compile:
var verificationResponse = await response.Content.ReadAsAsync<ReCAPTCHAVerificationResponse>();
Somewhere I found the suggestion to use:
var verificationResponse = await JsonSerializer.DeserializeAsync<ReCAPTCHAVerificationResponse>(await response.Content.ReadAsStreamAsync());
but it did not work. It compiled but did not provide a usable verificationResponse.
I got it to work by installing Microsoft.AspNet.WebApi.Client, but it is deprecated. Seems like there must be a better way.
If you're using Newtonsoft.Json, you're looking for something like
var content = await response.Content.ReadAsStreamAsync();
var response = JsonConvert.DeserializeObject<ReCAPTCHAVerificationResponse>(content);
If you're using System.Text.Json (Microsoft's flavor and recommended by them over Newtonsoft.Json for the most part)
var response = response.Content.ReadAsAsync<ReCAPTCHAVerificationResponse>();
However, this is not unique to Blazor nor .NET 5.