Initial certificate system

backend/app/services/captcha.py

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+import base64
+import io
+import random
+import secrets
+import string
+import time
+
+from PIL import Image, ImageDraw, ImageFont
+
+CAPTCHA_TTL_SECONDS = 300
+_captchas: dict[str, tuple[str, float]] = {}
+
+
+def make_captcha() -> dict[str, str]:
+    clean_expired_captchas()
+    captcha_id = secrets.token_urlsafe(16)
+    code = "".join(random.choice(string.ascii_uppercase + string.digits) for _ in range(4))
+    _captchas[captcha_id] = (code, time.time() + CAPTCHA_TTL_SECONDS)
+    return {"captcha_id": captcha_id, "image": draw_captcha_image(code)}
+
+
+def verify_captcha(captcha_id: str, captcha_code: str) -> bool:
+    clean_expired_captchas()
+    record = _captchas.pop(captcha_id, None)
+    if not record:
+        return False
+    expected, expires_at = record
+    if expires_at < time.time():
+        return False
+    return expected.upper() == captcha_code.strip().upper()
+
+
+def clean_expired_captchas() -> None:
+    now = time.time()
+    expired = [captcha_id for captcha_id, (_, expires_at) in _captchas.items() if expires_at < now]
+    for captcha_id in expired:
+        _captchas.pop(captcha_id, None)
+
+
+def draw_captcha_image(code: str) -> str:
+    width, height = 132, 44
+    image = Image.new("RGB", (width, height), "#f8fafc")
+    draw = ImageDraw.Draw(image)
+    font = ImageFont.load_default()
+    for i, char in enumerate(code):
+        draw.text((18 + i * 26, 13 + random.randint(-2, 2)), char, fill="#1f2937", font=font)
+    for _ in range(8):
+        x1, y1 = random.randint(0, width), random.randint(0, height)
+        x2, y2 = random.randint(0, width), random.randint(0, height)
+        draw.line((x1, y1, x2, y2), fill="#cbd5e1", width=1)
+
+    buffer = io.BytesIO()
+    image.save(buffer, format="PNG")
+    return "data:image/png;base64," + base64.b64encode(buffer.getvalue()).decode("ascii")