feat: Add authentication and personal user endpoint (#29)

* feat: Add authentication and personal user endpoint

This contribution adds a lot of scaffolding for the database fake
and testability of coderd.

A new endpoint "/user" is added to return the currently authenticated
user to the requester.

* Use TestMain to catch leak instead

* Add userpassword package

* Add WIP

* Add user auth

* Fix test

* Add comments

* Fix login response

* Fix order

* Fix generated code

* Update httpapi/httpapi.go

Co-authored-by: Bryan <bryan@coder.com>

Co-authored-by: Bryan <bryan@coder.com>

httpapi/httpapi.go

@@ -0,0 +1,114 @@
+package httpapi
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"reflect"
+	"regexp"
+	"strings"
+
+	"github.com/go-playground/validator/v10"
+)
+
+var (
+	validate      *validator.Validate
+	usernameRegex = regexp.MustCompile("^[a-zA-Z0-9]+(?:-[a-zA-Z0-9]+)*$")
+)
+
+// This init is used to create a validator and register validation-specific
+// functionality for the HTTP API.
+//
+// A single validator instance is used, because it caches struct parsing.
+func init() {
+	validate = validator.New()
+	validate.RegisterTagNameFunc(func(fld reflect.StructField) string {
+		name := strings.SplitN(fld.Tag.Get("json"), ",", 2)[0]
+		if name == "-" {
+			return ""
+		}
+		return name
+	})
+	validate.RegisterValidation("username", func(fl validator.FieldLevel) bool {
+		f := fl.Field().Interface()
+		str, ok := f.(string)
+		if !ok {
+			return false
+		}
+		if len(str) > 32 {
+			return false
+		}
+		if len(str) < 1 {
+			return false
+		}
+		return usernameRegex.MatchString(str)
+	})
+}
+
+// Response represents a generic HTTP response.
+type Response struct {
+	Message string  `json:"message" validate:"required"`
+	Errors  []Error `json:"errors,omitempty" validate:"required"`
+}
+
+// Error represents a scoped error to a user input.
+type Error struct {
+	Field string `json:"field" validate:"required"`
+	Code  string `json:"code" validate:"required"`
+}
+
+// Write outputs a standardized format to an HTTP response body.
+func Write(w http.ResponseWriter, status int, response Response) {
+	buf := &bytes.Buffer{}
+	enc := json.NewEncoder(buf)
+	enc.SetEscapeHTML(true)
+	err := enc.Encode(response)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	w.WriteHeader(status)
+	_, err = w.Write(buf.Bytes())
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+}
+
+// Read decodes JSON from the HTTP request into the value provided.
+// It uses go-validator to validate the incoming request body.
+func Read(rw http.ResponseWriter, r *http.Request, value interface{}) bool {
+	err := json.NewDecoder(r.Body).Decode(value)
+	if err != nil {
+		Write(rw, http.StatusBadRequest, Response{
+			Message: fmt.Sprintf("read body: %s", err.Error()),
+		})
+		return false
+	}
+	err = validate.Struct(value)
+	var validationErrors validator.ValidationErrors
+	if errors.As(err, &validationErrors) {
+		apiErrors := make([]Error, 0, len(validationErrors))
+		for _, validationError := range validationErrors {
+			apiErrors = append(apiErrors, Error{
+				Field: validationError.Field(),
+				Code:  validationError.Tag(),
+			})
+		}
+		Write(rw, http.StatusBadRequest, Response{
+			Message: "Validation failed",
+			Errors:  apiErrors,
+		})
+		return false
+	}
+	if err != nil {
+		Write(rw, http.StatusInternalServerError, Response{
+			Message: fmt.Sprintf("validation: %s", err.Error()),
+		})
+		return false
+	}
+	return true
+}