Support for HTTP GET requests

[tstocker-black-cape]

The GraphQL spec says that GET requests are allowed for queries

https://graphql.org/learn/serving-over-http/#get-request-and-parameters

The Spring GraphQL docs point to that document and seem to indicate that GET requests should work with a content type of application/graphql-response+json set.

https://docs.spring.io/spring-graphql/reference/transports.html

However, I can't get it to work with my server. I'm getting 405 errors back indicating that GET requests are NOT supported. Is there a way to make this work with Spring GraphQL?

[bclozel]

No we don't, this was discussed very early in the project, see #11.

Since then, things have moved on and the spec describes more clearly what's expected. This issue is a good opportunity to reconsider our stance. Unfortunately this is not just about adding a web handler, because we need to reject mutations so a broader revision is required.

We're thinking about introducing persisted queries support in the next minor version (see #1400, we'll probably create an umbrella issue for the broader support). If we decide to pursue this, we'll probably have to support GET requests anyway.