Implement login resolver (#15)

* add sign_up_method to users table

* add session store

* implement login resolver

server/utils/ginContext.go

@@ -0,0 +1,23 @@
+package utils
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/gin-gonic/gin"
+)
+
+func GinContextFromContext(ctx context.Context) (*gin.Context, error) {
+	ginContext := ctx.Value("GinContextKey")
+	if ginContext == nil {
+		err := fmt.Errorf("could not retrieve gin.Context")
+		return nil, err
+	}
+
+	gc, ok := ginContext.(*gin.Context)
+	if !ok {
+		err := fmt.Errorf("gin.Context has wrong type")
+		return nil, err
+	}
+	return gc, nil
+}