Разработчикам

# pip install requests jsonschema cryptography
import base64, json, requests, jsonschema
from urllib.parse import urlparse
from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PublicKey

SCHEMA = "https://паспорт-агента.рф/.well-known/agent-passport.schema.json"
b64d = lambda s: base64.urlsafe_b64decode(s + "=" * (-len(s) % 4))
b64e = lambda b: base64.urlsafe_b64encode(b).rstrip(b"=").decode()

def jcs(v):  # RFC 8785 для строк, целых чисел, true/false
    if isinstance(v, dict):
        ks = sorted(v, key=lambda k: k.encode("utf-16-be"))
        return "{" + ",".join(json.dumps(k, ensure_ascii=False) + ":" + jcs(v[k]) for k in ks) + "}"
    if isinstance(v, list):
        return "[" + ",".join(jcs(x) for x in v) + "]"
    return json.dumps(v, ensure_ascii=False)

def check(site):
    url = f"https://{site}/.well-known/agent-passport.json"
    p = requests.get(url, timeout=8).json()
    jsonschema.validate(p, requests.get(SCHEMA).json())
    assert urlparse(p["operator"]["site"]).hostname == site
    assert p["status"] == "active"
    level = "K2"
    for s in p.get("signatures", []):
        kid = json.loads(b64d(s["protected"]))["kid"]
        key = next(k for k in p["keys"] if k["kid"] == kid)
        body = {k: v for k, v in p.items() if k != "signatures"}
        msg = (s["protected"] + "." + b64e(jcs(body).encode())).encode()
        Ed25519PublicKey.from_public_bytes(b64d(key["x"])).verify(b64d(s["signature"]), msg)
        level = "K3"
    return level

$r = json_decode(file_get_contents(
    'https://xn----7sbbaom0ddhbmjqf.xn--p1ai/api/v1/check?url=' . urlencode('example.ru')
), true);
if ($r['ok']) {
    echo $r['level'], ' ', $r['passports'][0]['operator'];
} else {
    echo 'сделку не заключаем: ', $r['verdict_text'];
}