new file mode 100644
--- /dev/null
+++ b/src/event/quic/ngx_event_quic_openssl_compat.c
@@ -0,0 +1,646 @@
+
+/*
+ * Copyright (C) Nginx, Inc.
+ */
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_event.h>
+#include <ngx_event_quic_connection.h>
+
+
+#if (NGX_QUIC_OPENSSL_COMPAT)
+
+#define NGX_QUIC_COMPAT_RECORD_SIZE          1024
+
+#define NGX_QUIC_COMPAT_SSL_TP_EXT           0x39
+
+#define NGX_QUIC_COMPAT_CLIENT_HANDSHAKE     "CLIENT_HANDSHAKE_TRAFFIC_SECRET"
+#define NGX_QUIC_COMPAT_SERVER_HANDSHAKE     "SERVER_HANDSHAKE_TRAFFIC_SECRET"
+#define NGX_QUIC_COMPAT_CLIENT_APPLICATION   "CLIENT_TRAFFIC_SECRET_0"
+#define NGX_QUIC_COMPAT_SERVER_APPLICATION   "SERVER_TRAFFIC_SECRET_0"
+
+
+typedef struct {
+    ngx_quic_secret_t             secret;
+    ngx_uint_t                    cipher;
+} ngx_quic_compat_keys_t;
+
+
+typedef struct {
+    ngx_log_t                    *log;
+
+    u_char                        type;
+    ngx_str_t                     payload;
+    uint64_t                      number;
+    ngx_quic_compat_keys_t       *keys;
+
+    enum ssl_encryption_level_t   level;
+} ngx_quic_compat_record_t;
+
+
+struct ngx_quic_compat_s {
+    const SSL_QUIC_METHOD        *method;
+
+    enum ssl_encryption_level_t   write_level;
+    enum ssl_encryption_level_t   read_level;
+
+    uint64_t                      read_record;
+    ngx_quic_compat_keys_t        keys;
+
+    ngx_str_t                     tp;
+    ngx_str_t                     ctp;
+};
+
+
+static void ngx_quic_compat_keylog_callback(const SSL *ssl, const char *line);
+static ngx_int_t ngx_quic_compat_set_encryption_secret(ngx_log_t *log,
+    ngx_quic_compat_keys_t *keys, enum ssl_encryption_level_t level,
+    const SSL_CIPHER *cipher, const uint8_t *secret, size_t secret_len);
+static int ngx_quic_compat_add_transport_params_callback(SSL *ssl,
+    unsigned int ext_type, unsigned int context, const unsigned char **out,
+    size_t *outlen, X509 *x, size_t chainidx, int *al, void *add_arg);
+static int ngx_quic_compat_parse_transport_params_callback(SSL *ssl,
+    unsigned int ext_type, unsigned int context, const unsigned char *in,
+    size_t inlen, X509 *x, size_t chainidx, int *al, void *parse_arg);
+static void ngx_quic_compat_message_callback(int write_p, int version,
+    int content_type, const void *buf, size_t len, SSL *ssl, void *arg);
+static size_t ngx_quic_compat_create_header(ngx_quic_compat_record_t *rec,
+    u_char *out, ngx_uint_t plain);
+static ngx_int_t ngx_quic_compat_create_record(ngx_quic_compat_record_t *rec,
+    ngx_str_t *res);
+
+
+ngx_int_t
+ngx_quic_compat_init(ngx_conf_t *cf, SSL_CTX *ctx)
+{
+    SSL_CTX_set_keylog_callback(ctx, ngx_quic_compat_keylog_callback);
+
+    if (SSL_CTX_has_client_custom_ext(ctx, NGX_QUIC_COMPAT_SSL_TP_EXT)) {
+        return NGX_OK;
+    }
+
+    if (SSL_CTX_add_custom_ext(ctx, NGX_QUIC_COMPAT_SSL_TP_EXT,
+                               SSL_EXT_CLIENT_HELLO
+                               |SSL_EXT_TLS1_3_ENCRYPTED_EXTENSIONS,
+                               ngx_quic_compat_add_transport_params_callback,
+                               NULL,
+                               NULL,
+                               ngx_quic_compat_parse_transport_params_callback,
+                               NULL)
+        == 0)
+    {
+        ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
+                      "SSL_CTX_add_custom_ext() failed");
+        return NGX_ERROR;
+    }
+
+    return NGX_OK;
+}
+
+
+static void
+ngx_quic_compat_keylog_callback(const SSL *ssl, const char *line)
+{
+    u_char                        ch, *p, *start, value;
+    size_t                        n;
+    ngx_uint_t                    write;
+    const SSL_CIPHER             *cipher;
+    ngx_quic_compat_t            *com;
+    ngx_connection_t             *c;
+    ngx_quic_connection_t        *qc;
+    enum ssl_encryption_level_t   level;
+    u_char                        secret[EVP_MAX_MD_SIZE];
+
+    c = ngx_ssl_get_connection(ssl);
+    if (c->type != SOCK_DGRAM) {
+        return;
+    }
+
+    p = (u_char *) line;
+
+    for (start = p; *p && *p != ' '; p++);
+
+    n = p - start;
+
+    ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                   "quic compat secret %*s", n, start);
+
+    if (n == sizeof(NGX_QUIC_COMPAT_CLIENT_HANDSHAKE) - 1
+        && ngx_strncmp(start, NGX_QUIC_COMPAT_CLIENT_HANDSHAKE, n) == 0)
+    {
+        level = ssl_encryption_handshake;
+        write = 0;
+
+    } else if (n == sizeof(NGX_QUIC_COMPAT_SERVER_HANDSHAKE) - 1
+               && ngx_strncmp(start, NGX_QUIC_COMPAT_SERVER_HANDSHAKE, n) == 0)
+    {
+        level = ssl_encryption_handshake;
+        write = 1;
+
+    } else if (n == sizeof(NGX_QUIC_COMPAT_CLIENT_APPLICATION) - 1
+               && ngx_strncmp(start, NGX_QUIC_COMPAT_CLIENT_APPLICATION, n)
+                  == 0)
+    {
+        level = ssl_encryption_application;
+        write = 0;
+
+    } else if (n == sizeof(NGX_QUIC_COMPAT_SERVER_APPLICATION) - 1
+               && ngx_strncmp(start, NGX_QUIC_COMPAT_SERVER_APPLICATION, n)
+                   == 0)
+    {
+        level = ssl_encryption_application;
+        write = 1;
+
+    } else {
+        return;
+    }
+
+    if (*p++ == '\0') {
+        return;
+    }
+
+    for ( /* void */ ; *p && *p != ' '; p++);
+
+    if (*p++ == '\0') {
+        return;
+    }
+
+    for (n = 0, start = p; *p; p++) {
+        ch = *p;
+
+        if (ch >= '0' && ch <= '9') {
+            value = ch - '0';
+            goto next;
+        }
+
+        ch = (u_char) (ch | 0x20);
+
+        if (ch >= 'a' && ch <= 'f') {
+            value = ch - 'a' + 10;
+            goto next;
+        }
+
+        ngx_log_error(NGX_LOG_EMERG, c->log, 0,
+                      "invalid OpenSSL QUIC secret format");
+
+        return;
+
+    next:
+
+        if ((p - start) % 2) {
+            secret[n++] += value;
+
+        } else {
+            if (n >= EVP_MAX_MD_SIZE) {
+                ngx_log_error(NGX_LOG_EMERG, c->log, 0,
+                              "too big OpenSSL QUIC secret");
+                return;
+            }
+
+            secret[n] = (value << 4);
+        }
+    }
+
+    qc = ngx_quic_get_connection(c);
+    com = qc->compat;
+    cipher = SSL_get_current_cipher(ssl);
+
+    if (write) {
+        com->method->set_write_secret((SSL *) ssl, level, cipher, secret, n);
+        com->write_level = level;
+
+    } else {
+        com->method->set_read_secret((SSL *) ssl, level, cipher, secret, n);
+        com->read_level = level;
+        com->read_record = 0;
+
+        (void) ngx_quic_compat_set_encryption_secret(c->log, &com->keys, level,
+                                                     cipher, secret, n);
+    }
+}
+
+
+static ngx_int_t
+ngx_quic_compat_set_encryption_secret(ngx_log_t *log,
+    ngx_quic_compat_keys_t *keys, enum ssl_encryption_level_t level,
+    const SSL_CIPHER *cipher, const uint8_t *secret, size_t secret_len)
+{
+    ngx_int_t            key_len;
+    ngx_str_t            secret_str;
+    ngx_uint_t           i;
+    ngx_quic_hkdf_t      seq[2];
+    ngx_quic_secret_t   *peer_secret;
+    ngx_quic_ciphers_t   ciphers;
+
+    peer_secret = &keys->secret;
+
+    keys->cipher = SSL_CIPHER_get_id(cipher);
+
+    key_len = ngx_quic_ciphers(keys->cipher, &ciphers, level);
+
+    if (key_len == NGX_ERROR) {
+        ngx_ssl_error(NGX_LOG_INFO, log, 0, "unexpected cipher");
+        return NGX_ERROR;
+    }
+
+    if (sizeof(peer_secret->secret.data) < secret_len) {
+        ngx_log_error(NGX_LOG_ALERT, log, 0,
+                      "unexpected secret len: %uz", secret_len);
+        return NGX_ERROR;
+    }
+
+    peer_secret->secret.len = secret_len;
+    ngx_memcpy(peer_secret->secret.data, secret, secret_len);
+
+    peer_secret->key.len = key_len;
+    peer_secret->iv.len = NGX_QUIC_IV_LEN;
+
+    secret_str.len = secret_len;
+    secret_str.data = (u_char *) secret;
+
+    ngx_quic_hkdf_set(&seq[0], "tls13 key", &peer_secret->key, &secret_str);
+    ngx_quic_hkdf_set(&seq[1], "tls13 iv", &peer_secret->iv, &secret_str);
+
+    for (i = 0; i < (sizeof(seq) / sizeof(seq[0])); i++) {
+        if (ngx_quic_hkdf_expand(&seq[i], ciphers.d, log) != NGX_OK) {
+            return NGX_ERROR;
+        }
+    }
+
+    return NGX_OK;
+}
+
+
+static int
+ngx_quic_compat_add_transport_params_callback(SSL *ssl, unsigned int ext_type,
+    unsigned int context, const unsigned char **out, size_t *outlen, X509 *x,
+    size_t chainidx, int *al, void *add_arg)
+{
+    ngx_connection_t       *c;
+    ngx_quic_compat_t      *com;
+    ngx_quic_connection_t  *qc;
+
+    c = ngx_ssl_get_connection(ssl);
+    if (c->type != SOCK_DGRAM) {
+        return 0;
+    }
+
+    ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                   "quic compat add transport params");
+
+    qc = ngx_quic_get_connection(c);
+    com = qc->compat;
+
+    *out = com->tp.data;
+    *outlen = com->tp.len;
+
+    return 1;
+}
+
+
+static int
+ngx_quic_compat_parse_transport_params_callback(SSL *ssl, unsigned int ext_type,
+    unsigned int context, const unsigned char *in, size_t inlen, X509 *x,
+    size_t chainidx, int *al, void *parse_arg)
+{
+    u_char                 *p;
+    ngx_connection_t       *c;
+    ngx_quic_compat_t      *com;
+    ngx_quic_connection_t  *qc;
+
+    c = ngx_ssl_get_connection(ssl);
+    if (c->type != SOCK_DGRAM) {
+        return 0;
+    }
+
+    ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                   "quic compat parse transport params");
+
+    qc = ngx_quic_get_connection(c);
+    com = qc->compat;
+
+    p = ngx_pnalloc(c->pool, inlen);
+    if (p == NULL) {
+        return 0;
+    }
+
+    ngx_memcpy(p, in, inlen);
+
+    com->ctp.data = p;
+    com->ctp.len = inlen;
+
+    return 1;
+}
+
+
+int
+SSL_set_quic_method(SSL *ssl, const SSL_QUIC_METHOD *quic_method)
+{
+    BIO                    *rbio, *wbio;
+    ngx_connection_t       *c;
+    ngx_quic_compat_t      *com;
+    ngx_quic_connection_t  *qc;
+
+    c = ngx_ssl_get_connection(ssl);
+
+    ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, 0, "quic compat set method");
+
+    qc = ngx_quic_get_connection(c);
+
+    qc->compat = ngx_pcalloc(c->pool, sizeof(ngx_quic_compat_t));
+    if (qc->compat == NULL) {
+        return 0;
+    }
+
+    com = qc->compat;
+    com->method = quic_method;
+
+    rbio = BIO_new(BIO_s_mem());
+    if (rbio == NULL) {
+        return 0;
+    }
+
+    wbio = BIO_new(BIO_s_null());
+    if (wbio == NULL) {
+        return 0;
+    }
+
+    SSL_set_bio(ssl, rbio, wbio);
+
+    SSL_set_msg_callback(ssl, ngx_quic_compat_message_callback);
+
+    /* early data is not supported */
+    SSL_set_max_early_data(ssl, 0);
+
+    return 1;
+}
+
+
+static void
+ngx_quic_compat_message_callback(int write_p, int version, int content_type,
+    const void *buf, size_t len, SSL *ssl, void *arg)
+{
+    ngx_uint_t                    alert;
+    ngx_connection_t             *c;
+    ngx_quic_compat_t            *com;
+    ngx_quic_connection_t        *qc;
+    enum ssl_encryption_level_t   level;
+
+    if (!write_p) {
+        return;
+    }
+
+    c = ngx_ssl_get_connection(ssl);
+    qc = ngx_quic_get_connection(c);
+
+    if (qc == NULL) {
+        /* closing */
+        return;
+    }
+
+    com = qc->compat;
+    level = com->write_level;
+
+    switch (content_type) {
+
+    case SSL3_RT_HANDSHAKE:
+        ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                       "quic compat tx %s len:%uz ",
+                       ngx_quic_level_name(level), len);
+
+        (void) com->method->add_handshake_data(ssl, level, buf, len);
+
+        break;
+
+    case SSL3_RT_ALERT:
+        if (len >= 2) {
+            alert = ((u_char *) buf)[1];
+
+            ngx_log_debug3(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                           "quic compat %s alert:%ui len:%uz ",
+                           ngx_quic_level_name(level), alert, len);
+
+            (void) com->method->send_alert(ssl, level, alert);
+        }
+
+        break;
+    }
+}
+
+
+int
+SSL_provide_quic_data(SSL *ssl, enum ssl_encryption_level_t level,
+    const uint8_t *data, size_t len)
+{
+    BIO                       *rbio;
+    size_t                     n;
+    u_char                    *p;
+    ngx_str_t                  res;
+    ngx_connection_t          *c;
+    ngx_quic_compat_t         *com;
+    ngx_quic_connection_t     *qc;
+    ngx_quic_compat_record_t   rec;
+    u_char                     in[NGX_QUIC_COMPAT_RECORD_SIZE + 1];
+    u_char                     out[NGX_QUIC_COMPAT_RECORD_SIZE + 1
+                                   + SSL3_RT_HEADER_LENGTH
+                                   + EVP_GCM_TLS_TAG_LEN];
+
+    c = ngx_ssl_get_connection(ssl);
+
+    ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0, "quic compat rx %s len:%uz",
+                   ngx_quic_level_name(level), len);
+
+    qc = ngx_quic_get_connection(c);
+    com = qc->compat;
+    rbio = SSL_get_rbio(ssl);
+
+    while (len) {
+        ngx_memzero(&rec, sizeof(ngx_quic_compat_record_t));
+
+        rec.type = SSL3_RT_HANDSHAKE;
+        rec.log = c->log;
+        rec.number = com->read_record++;
+        rec.keys = &com->keys;
+
+        if (level == ssl_encryption_initial) {
+            n = ngx_min(len, 65535);
+
+            rec.payload.len = n;
+            rec.payload.data = (u_char *) data;
+
+            ngx_quic_compat_create_header(&rec, out, 1);
+
+            BIO_write(rbio, out, SSL3_RT_HEADER_LENGTH);
+            BIO_write(rbio, data, n);
+
+#if defined(NGX_QUIC_DEBUG_CRYPTO) && defined(NGX_QUIC_DEBUG_PACKETS)
+            ngx_log_debug5(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                           "quic compat record len:%uz %*xs%*xs",
+                           n + SSL3_RT_HEADER_LENGTH,
+                           (size_t) SSL3_RT_HEADER_LENGTH, out, n, data);
+#endif
+
+        } else {
+            n = ngx_min(len, NGX_QUIC_COMPAT_RECORD_SIZE);
+
+            p = ngx_cpymem(in, data, n);
+            *p++ = SSL3_RT_HANDSHAKE;
+
+            rec.payload.len = p - in;
+            rec.payload.data = in;
+
+            res.data = out;
+
+            if (ngx_quic_compat_create_record(&rec, &res) != NGX_OK) {
+                return 0;
+            }
+
+#if defined(NGX_QUIC_DEBUG_CRYPTO) && defined(NGX_QUIC_DEBUG_PACKETS)
+            ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                           "quic compat record len:%uz %xV", res.len, &res);
+#endif
+
+            BIO_write(rbio, res.data, res.len);
+        }
+
+        data += n;
+        len -= n;
+    }
+
+    return 1;
+}
+
+
+static size_t
+ngx_quic_compat_create_header(ngx_quic_compat_record_t *rec, u_char *out,
+    ngx_uint_t plain)
+{
+    u_char  type;
+    size_t  len;
+
+    len = rec->payload.len;
+
+    if (plain) {
+        type = rec->type;
+
+    } else {
+        type = SSL3_RT_APPLICATION_DATA;
+        len += EVP_GCM_TLS_TAG_LEN;
+    }
+
+    out[0] = type;
+    out[1] = 0x03;
+    out[2] = 0x03;
+    out[3] = (len >> 8);
+    out[4] = len;
+
+    return 5;
+}
+
+
+static ngx_int_t
+ngx_quic_compat_create_record(ngx_quic_compat_record_t *rec, ngx_str_t *res)
+{
+    ngx_str_t            ad, out;
+    ngx_quic_secret_t   *secret;
+    ngx_quic_ciphers_t   ciphers;
+    u_char               nonce[NGX_QUIC_IV_LEN];
+
+    ad.data = res->data;
+    ad.len = ngx_quic_compat_create_header(rec, ad.data, 0);
+
+    out.len = rec->payload.len + EVP_GCM_TLS_TAG_LEN;
+    out.data = res->data + ad.len;
+
+#ifdef NGX_QUIC_DEBUG_CRYPTO
+    ngx_log_debug2(NGX_LOG_DEBUG_EVENT, rec->log, 0,
+                   "quic compat ad len:%uz %xV", ad.len, &ad);
+#endif
+
+    if (ngx_quic_ciphers(rec->keys->cipher, &ciphers, rec->level) == NGX_ERROR)
+    {
+        return NGX_ERROR;
+    }
+
+    secret = &rec->keys->secret;
+
+    ngx_memcpy(nonce, secret->iv.data, secret->iv.len);
+    ngx_quic_compute_nonce(nonce, sizeof(nonce), rec->number);
+
+    if (ngx_quic_tls_seal(ciphers.c, secret, &out,
+                          nonce, &rec->payload, &ad, rec->log)
+        != NGX_OK)
+    {
+        return NGX_ERROR;
+    }
+
+    res->len = ad.len + out.len;
+
+    return NGX_OK;
+}
+
+
+enum ssl_encryption_level_t
+SSL_quic_read_level(const SSL *ssl)
+{
+    ngx_connection_t       *c;
+    ngx_quic_connection_t  *qc;
+
+    c = ngx_ssl_get_connection(ssl);
+    qc = ngx_quic_get_connection(c);
+
+    return qc->compat->read_level;
+}
+
+
+enum ssl_encryption_level_t
+SSL_quic_write_level(const SSL *ssl)
+{
+    ngx_connection_t       *c;
+    ngx_quic_connection_t  *qc;
+
+    c = ngx_ssl_get_connection(ssl);
+    qc = ngx_quic_get_connection(c);
+
+    return qc->compat->write_level;
+}
+
+
+int
+SSL_set_quic_transport_params(SSL *ssl, const uint8_t *params,
+    size_t params_len)
+{
+    ngx_connection_t       *c;
+    ngx_quic_compat_t      *com;
+    ngx_quic_connection_t  *qc;
+
+    c = ngx_ssl_get_connection(ssl);
+    qc = ngx_quic_get_connection(c);
+    com = qc->compat;
+
+    com->tp.len = params_len;
+    com->tp.data = (u_char *) params;
+
+    return 1;
+}
+
+
+void
+SSL_get_peer_quic_transport_params(const SSL *ssl, const uint8_t **out_params,
+    size_t *out_params_len)
+{
+    ngx_connection_t       *c;
+    ngx_quic_compat_t      *com;
+    ngx_quic_connection_t  *qc;
+
+    c = ngx_ssl_get_connection(ssl);
+    qc = ngx_quic_get_connection(c);
+    com = qc->compat;
+
+    *out_params = com->ctp.data;
+    *out_params_len = com->ctp.len;
+}
+
+#endif /* NGX_QUIC_OPENSSL_COMPAT */