fix(codegen): dedupe security schemes by type

[disintegrator]

This commit solves a bug where designs that use multiple security schemes of the same type break the generated Auther interface for a service as well as endpoint-related init methods due to unnecessary code duplication from ranging over .Schemes.

Reproducer

import (
	. "goa.design/goa/v3/dsl"
)

var AcmeAPIKey = APIKeySecurity("acme_api_key")
var AcmeTenant = APIKeySecurity("acme_tenant_id")

var _ = Service("customers", func() {
	Security(AcmeAPIKey, AcmeTenant)

        // ...
})

This currently results in code like this:

// Auther defines the authorization functions to be implemented by the service.
type Auther interface {
	// APIKeyAuth implements the authorization logic for the APIKey security scheme.
	APIKeyAuth(ctx context.Context, key string, schema *security.APIKeyScheme) (context.Context, error)
	// APIKeyAuth implements the authorization logic for the APIKey security scheme.
	APIKeyAuth(ctx context.Context, key string, schema *security.APIKeyScheme) (context.Context, error)
}

And:

// NewEndpoints wraps the methods of the "assets" service with endpoints.
func NewEndpoints(s Service) *Endpoints {
	// Casting service to Auther interface
	a := s.(Auther)
	return &Endpoints{
		UploadOpenAPIv3: NewUpdateDetailsEndpoint(s, a.APIKeyAuth, a.APIKeyAuth),
		//                                                         ^ 🚨
	}
}

// ...

func NewUpdateDetailsEndpoint(s Service, authAPIKeyFn security.AuthAPIKeyFunc, authAPIKeyFn security.AuthAPIKeyFunc) goa.Endpoint {
//                                                                             ^ 🚨
	// ...
}

[disintegrator]

Just need to figure out testing but putting it up PR to start discussion.

[raphael]

Thank you for the PR, it looks great. Will be happy to merge once there's a test for it.

[raphael]

This is a good bug fix that I'd like to have in the next release of Goa, let me know if I can help with the tests.

[disintegrator]

@raphael sorry for the delay, i've been a little swamped. I'll set some time aside for writing tests this week.

[disintegrator]

Hey @raphael, added a couple of test DSLs to the mix that should reproduce this bug and confirm it's fixed by this PR.

[raphael]

Awesome, thank you