Add directives docs

docs/content/directives.md

@@ -0,0 +1,63 @@
+---
+title: Using schema directives to implement permission checks
+description: Implementing graphql schema directives in golang for permission checks.  
+linkTitle: Schema Directives
+menu: main
+---
+
+Directives are a bit like annotations in any other language. They give you a way to specify some behaviour without directly binding to the implementation. This can be really useful for cross cutting concerns like permission checks.
+
+**Note**: The current directives implementation is still fairly limited, and is designed to cover the most common "field middleware" case.
+
+## Declare it in the schema
+
+Directives are declared in your schema, along with all your other types. Lets define a @hasRole directive:
+
+```graphql
+directive @hasRole(role: Role!) on FIELD_DEFINITION
+
+enum Role {
+    ADMIN
+    USER
+}
+```
+
+When we next run go generate, gqlgen will add this directive to the DirectiveRoot 
+```go
+type DirectiveRoot struct {
+	HasRole func(ctx context.Context, next graphql.Resolver, role Role) (res interface{}, err error)
+}
+```
+
+
+## Use it in the schema
+
+We can call this on any field definition now:
+```graphql
+type Mutation {
+	deleteUser(userID: ID!): Bool @hasRole(role: ADMIN)
+}
+```
+
+## Implement the directive
+
+Finally, we need to implement the directive, and pass it in when startin gthe server:
+```go
+package main
+
+func main() {
+	c := Config{ Resolvers: &resolvers{} }
+	c.Directives.HasRole = func(ctx context.Context, next graphql.Resolver, role Role) (interface{}, error) {
+		if !getCurrentUser(ctx).HasRole(role) {
+			// block calling the next resolver
+			return nil, fmt.Errorf("Access denied")
+		}
+
+		// or let it pass through
+		return next(ctx)
+	}
+
+	http.Handle("/query", handler.GraphQL(todo.NewExecutableSchema(c), ))
+	log.Fatal(http.ListenAndServe(":8081", nil))
+}
+```

docs/static/main.css

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 }
 
 .content {
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+    max-width: 920px;
     margin: auto;
 }