1.安装caddy

sudo apt update
sudo apt install -y debian-keyring debian-archive-keyring apt-transport-https curl

# 添加 Caddy 官方 GPG key
curl -1sLf 'https://dl.cloudsmith.io/public/caddy/stable/gpg.key' | sudo tee /etc/apt/trusted.gpg.d/caddy-stable.asc

# 添加 Caddy 官方 APT 源
curl -1sLf 'https://dl.cloudsmith.io/public/caddy/stable/debian.deb.txt' | sudo tee /etc/apt/sources.list.d/caddy-stable.list

# 安装
sudo apt update
sudo apt install -y caddy

2.如果遇到报错

# 1) 清理旧配置（如果不存在也没关系）
sudo rm -f /etc/apt/sources.list.d/caddy-stable.list
sudo rm -f /etc/apt/trusted.gpg.d/caddy-stable.asc

# 2) 放置新 key（dearmor 到 keyrings）
sudo mkdir -p /etc/apt/keyrings
curl -fsSL https://dl.cloudsmith.io/public/caddy/stable/gpg.key \
  | sudo gpg --dearmor -o /etc/apt/keyrings/caddy-stable-archive-keyring.gpg

# 3) 正确写入 APT 源（Ubuntu 22.04 = jammy）
echo "deb [signed-by=/etc/apt/keyrings/caddy-stable-archive-keyring.gpg] \
https://dl.cloudsmith.io/public/caddy/stable/deb/ubuntu jammy main" \
| sudo tee /etc/apt/sources.list.d/caddy-stable.list > /dev/null

echo "deb-src [signed-by=/etc/apt/keyrings/caddy-stable-archive-keyring.gpg] \
https://dl.cloudsmith.io/public/caddy/stable/deb/ubuntu jammy main" \
| sudo tee -a /etc/apt/sources.list.d/caddy-stable.list > /dev/null

# 4) 更新并安装
sudo apt update
sudo apt install -y caddy

# （可选）确认版本
caddy version

3.配置反代

vi /etc/caddy/Caddyfile

mail.example.com {
    reverse_proxy 127.0.0.1:18080
}

配置好之后Caddy会自动申请并配置HTTPS证书

4.测试与生效

检查配置是否正确：

sudo caddy validate --config /etc/caddy/Caddyfile

重新加载 Caddy：

sudo systemctl reload caddy