Add authentication function

Signed-off-by: Asai Neko <sugar@sne.moe>

pkgs/email/resend.go

@@ -0,0 +1,87 @@
+package email
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"time"
+
+	"github.com/spf13/viper"
+)
+
+type Client struct {
+	apiKey string
+	http   *http.Client
+}
+
+// Resend service client
+func NewResendClient() (*Client, error) {
+	key := viper.GetString("email.resend_api_key")
+	if key == "" {
+		return nil, errors.New("RESEND_API_KEY not set")
+	}
+
+	return &Client{
+		apiKey: key,
+		http: &http.Client{
+			Timeout: 10 * time.Second,
+		},
+	}, nil
+}
+
+type sendEmailRequest struct {
+	From    string   `json:"from"`
+	To      []string `json:"to"`
+	Subject string   `json:"subject"`
+	HTML    string   `json:"html,omitempty"`
+	Text    string   `json:"text,omitempty"`
+}
+
+type sendEmailResponse struct {
+	ID string `json:"id"`
+}
+
+// Send email by resend API
+func (c *Client) Send(to, subject, html string) (string, error) {
+	reqBody := sendEmailRequest{
+		From:    viper.GetString("email.from"),
+		To:      []string{to},
+		Subject: subject,
+		HTML:    html,
+	}
+
+	body, err := json.Marshal(reqBody)
+	if err != nil {
+		return "", err
+	}
+
+	req, err := http.NewRequest(
+		http.MethodPost,
+		"https://api.resend.com/emails",
+		bytes.NewReader(body),
+	)
+	if err != nil {
+		return "", err
+	}
+
+	req.Header.Set("Authorization", "Bearer "+c.apiKey)
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode >= 300 {
+		return "", errors.New("resend send failed")
+	}
+
+	var res sendEmailResponse
+	if err := json.NewDecoder(resp.Body).Decode(&res); err != nil {
+		return "", err
+	}
+
+	return res.ID, nil
+}