diff --git a/library/ssl_client.c b/library/ssl_client.c
index 0c32f07..22ca57c 100644
--- a/library/ssl_client.c
+++ b/library/ssl_client.c
@@ -308,110 +308,6 @@
 #endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C ||
           MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
 
-#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
-/*
- * Function for writing a signature algorithm extension.
- *
- * The `extension_data` field of signature algorithm contains  a `SignatureSchemeList`
- * value (TLS 1.3 RFC8446):
- *      enum {
- *         ....
- *        ecdsa_secp256r1_sha256( 0x0403 ),
- *        ecdsa_secp384r1_sha384( 0x0503 ),
- *        ecdsa_secp521r1_sha512( 0x0603 ),
- *         ....
- *      } SignatureScheme;
- *
- *      struct {
- *         SignatureScheme supported_signature_algorithms<2..2^16-2>;
- *      } SignatureSchemeList;
- *
- * The `extension_data` field of signature algorithm contains a `SignatureAndHashAlgorithm`
- * value (TLS 1.2 RFC5246):
- *      enum {
- *          none(0), md5(1), sha1(2), sha224(3), sha256(4), sha384(5),
- *          sha512(6), (255)
- *      } HashAlgorithm;
- *
- *      enum { anonymous(0), rsa(1), dsa(2), ecdsa(3), (255) }
- *        SignatureAlgorithm;
- *
- *      struct {
- *          HashAlgorithm hash;
- *          SignatureAlgorithm signature;
- *      } SignatureAndHashAlgorithm;
- *
- *      SignatureAndHashAlgorithm
- *        supported_signature_algorithms<2..2^16-2>;
- *
- * The TLS 1.3 signature algorithm extension was defined to be a compatible
- * generalization of the TLS 1.2 signature algorithm extension.
- * `SignatureAndHashAlgorithm` field of TLS 1.2 can be represented by
- * `SignatureScheme` field of TLS 1.3
- *
- */
-static int ssl_write_sig_alg_ext( mbedtls_ssl_context *ssl, unsigned char *buf,
-                                  const unsigned char *end, size_t *out_len )
-{
-    unsigned char *p = buf;
-    unsigned char *supported_sig_alg; /* Start of supported_signature_algorithms */
-    size_t supported_sig_alg_len = 0; /* Length of supported_signature_algorithms */
-
-    *out_len = 0;
-
-    MBEDTLS_SSL_DEBUG_MSG( 3, ( "adding signature_algorithms extension" ) );
-
-    /* Check if we have space for header and length field:
-     * - extension_type         (2 bytes)
-     * - extension_data_length  (2 bytes)
-     * - supported_signature_algorithms_length   (2 bytes)
-     */
-    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 6 );
-    p += 6;
-
-    /*
-     * Write supported_signature_algorithms
-     */
-    supported_sig_alg = p;
-    const uint16_t *sig_alg = mbedtls_ssl_get_sig_algs( ssl );
-    if( sig_alg == NULL )
-        return( MBEDTLS_ERR_SSL_BAD_CONFIG );
-
-    for( ; *sig_alg != MBEDTLS_TLS1_3_SIG_NONE; sig_alg++ )
-    {
-        if( ! mbedtls_ssl_sig_alg_is_supported( ssl, *sig_alg ) )
-            continue;
-        MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
-        MBEDTLS_PUT_UINT16_BE( *sig_alg, p, 0 );
-        p += 2;
-        MBEDTLS_SSL_DEBUG_MSG( 3, ( "signature scheme [%x]", *sig_alg ) );
-    }
-
-    /* Length of supported_signature_algorithms */
-    supported_sig_alg_len = p - supported_sig_alg;
-    if( supported_sig_alg_len == 0 )
-    {
-        MBEDTLS_SSL_DEBUG_MSG( 1, ( "No signature algorithms defined." ) );
-        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
-    }
-
-    /* Write extension_type */
-    MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_SIG_ALG, buf, 0 );
-    /* Write extension_data_length */
-    MBEDTLS_PUT_UINT16_BE( supported_sig_alg_len + 2, buf, 2 );
-    /* Write length of supported_signature_algorithms */
-    MBEDTLS_PUT_UINT16_BE( supported_sig_alg_len, buf, 4 );
-
-    /* Output the total length of signature algorithms extension. */
-    *out_len = p - buf;
-
-#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
-    ssl->handshake->extensions_present |= MBEDTLS_SSL_EXT_SIG_ALG;
-#endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
-    return( 0 );
-}
-#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
-
 static int ssl_write_client_hello_cipher_suites(
             mbedtls_ssl_context *ssl,
             unsigned char *buf,
@@ -721,7 +617,7 @@
 #endif
        0 )
     {
-        ret = ssl_write_sig_alg_ext( ssl, p, end, &output_len );
+        ret = mbedtls_ssl_write_sig_alg_ext( ssl, p, end, &output_len );
         if( ret != 0 )
             return( ret );
         p += output_len;
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index e8acc23..4d8c479 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -2290,4 +2290,7 @@
     mbedtls_ssl_protocol_version min_tls_version,
     mbedtls_ssl_protocol_version max_tls_version );
 
+int mbedtls_ssl_write_sig_alg_ext( mbedtls_ssl_context *ssl, unsigned char *buf,
+                                   const unsigned char *end, size_t *out_len );
+
 #endif /* ssl_misc.h */
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 250bae9..d187585 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -7998,4 +7998,104 @@
     return( 0 );
 }
 
+#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
+/*
+ * Function for writing a signature algorithm extension.
+ *
+ * The `extension_data` field of signature algorithm contains  a `SignatureSchemeList`
+ * value (TLS 1.3 RFC8446):
+ *      enum {
+ *         ....
+ *        ecdsa_secp256r1_sha256( 0x0403 ),
+ *        ecdsa_secp384r1_sha384( 0x0503 ),
+ *        ecdsa_secp521r1_sha512( 0x0603 ),
+ *         ....
+ *      } SignatureScheme;
+ *
+ *      struct {
+ *         SignatureScheme supported_signature_algorithms<2..2^16-2>;
+ *      } SignatureSchemeList;
+ *
+ * The `extension_data` field of signature algorithm contains a `SignatureAndHashAlgorithm`
+ * value (TLS 1.2 RFC5246):
+ *      enum {
+ *          none(0), md5(1), sha1(2), sha224(3), sha256(4), sha384(5),
+ *          sha512(6), (255)
+ *      } HashAlgorithm;
+ *
+ *      enum { anonymous(0), rsa(1), dsa(2), ecdsa(3), (255) }
+ *        SignatureAlgorithm;
+ *
+ *      struct {
+ *          HashAlgorithm hash;
+ *          SignatureAlgorithm signature;
+ *      } SignatureAndHashAlgorithm;
+ *
+ *      SignatureAndHashAlgorithm
+ *        supported_signature_algorithms<2..2^16-2>;
+ *
+ * The TLS 1.3 signature algorithm extension was defined to be a compatible
+ * generalization of the TLS 1.2 signature algorithm extension.
+ * `SignatureAndHashAlgorithm` field of TLS 1.2 can be represented by
+ * `SignatureScheme` field of TLS 1.3
+ *
+ */
+int mbedtls_ssl_write_sig_alg_ext( mbedtls_ssl_context *ssl, unsigned char *buf,
+                                   const unsigned char *end, size_t *out_len )
+{
+    unsigned char *p = buf;
+    unsigned char *supported_sig_alg; /* Start of supported_signature_algorithms */
+    size_t supported_sig_alg_len = 0; /* Length of supported_signature_algorithms */
+
+    *out_len = 0;
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "adding signature_algorithms extension" ) );
+
+    /* Check if we have space for header and length field:
+     * - extension_type         (2 bytes)
+     * - extension_data_length  (2 bytes)
+     * - supported_signature_algorithms_length   (2 bytes)
+     */
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 6 );
+    p += 6;
+
+    /*
+     * Write supported_signature_algorithms
+     */
+    supported_sig_alg = p;
+    const uint16_t *sig_alg = mbedtls_ssl_get_sig_algs( ssl );
+    if( sig_alg == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_CONFIG );
+
+    for( ; *sig_alg != MBEDTLS_TLS1_3_SIG_NONE; sig_alg++ )
+    {
+        if( ! mbedtls_ssl_sig_alg_is_supported( ssl, *sig_alg ) )
+            continue;
+        MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
+        MBEDTLS_PUT_UINT16_BE( *sig_alg, p, 0 );
+        p += 2;
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "signature scheme [%x]", *sig_alg ) );
+    }
+
+    /* Length of supported_signature_algorithms */
+    supported_sig_alg_len = p - supported_sig_alg;
+    if( supported_sig_alg_len == 0 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "No signature algorithms defined." ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_SIG_ALG, buf, 0 );
+    MBEDTLS_PUT_UINT16_BE( supported_sig_alg_len + 2, buf, 2 );
+    MBEDTLS_PUT_UINT16_BE( supported_sig_alg_len, buf, 4 );
+
+    *out_len = p - buf;
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
+    ssl->handshake->extensions_present |= MBEDTLS_SSL_EXT_SIG_ALG;
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
+    return( 0 );
+}
+#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
+
 #endif /* MBEDTLS_SSL_TLS_C */
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index b2a5cfc..775443c 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -25,6 +25,10 @@
 #include "mbedtls/error.h"
 #include "mbedtls/platform.h"
 
+#include "ssl_misc.h"
+#include "ssl_tls13_keys.h"
+#include "ssl_debug_helpers.h"
+
 #if defined(MBEDTLS_ECP_C)
 #include "mbedtls/ecp.h"
 #endif /* MBEDTLS_ECP_C */
@@ -1140,7 +1144,7 @@
     if( mbedtls_ssl_tls13_some_psk_enabled( ssl ) )
         mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_SERVER_FINISHED );
     else
-        mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_SERVER_CERTIFICATE );
+        mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_CERTIFICATE_REQUEST );
 #else
     mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_SERVER_FINISHED );
 #endif
@@ -1151,6 +1155,127 @@
     return( ret );
 }
 
+#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
+#define SSL_CERTIFICATE_REQUEST_SEND_REQUEST 0
+#define SSL_CERTIFICATE_REQUEST_SKIP         1
+/* Coordination:
+ * Check whether a CertificateRequest message should be written.
+ * Returns a negative code on failure, or
+ * - SSL_CERTIFICATE_REQUEST_SEND_REQUEST
+ * - SSL_CERTIFICATE_REQUEST_SKIP
+ * indicating if the writing of the CertificateRequest
+ * should be skipped or not.
+ */
+static int ssl_tls13_certificate_request_coordinate( mbedtls_ssl_context *ssl )
+{
+    int authmode;
+
+    authmode = ssl->conf->authmode;
+
+    if( authmode == MBEDTLS_SSL_VERIFY_NONE )
+        return( SSL_CERTIFICATE_REQUEST_SKIP );
+
+    return( SSL_CERTIFICATE_REQUEST_SEND_REQUEST );
+}
+
+/*
+ * struct {
+ *   opaque certificate_request_context<0..2^8-1>;
+ *   Extension extensions<2..2^16-1>;
+ * } CertificateRequest;
+ *
+ */
+static int ssl_tls13_write_certificate_request_body( mbedtls_ssl_context *ssl,
+                                                     unsigned char *buf,
+                                                     const unsigned char *end,
+                                                     size_t *out_len )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    unsigned char *p = buf;
+    size_t output_len = 0;
+    unsigned char *p_extensions_len;
+
+    *out_len = 0;
+
+    /* Check if we have enough space:
+     * - certificate_request_context (1 byte)
+     * - extensions length           (2 bytes)
+     */
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 3 );
+
+    /*
+     * Write certificate_request_context
+     */
+    /*
+     * We use a zero length context for the normal handshake
+     * messages. For post-authentication handshake messages
+     * this request context would be set to a non-zero value.
+     */
+    *p++ = 0x0;
+
+    /*
+     * Write extensions
+     */
+    /* The extensions must contain the signature_algorithms. */
+    p_extensions_len = p;
+    p += 2;
+    ret = mbedtls_ssl_write_sig_alg_ext( ssl, p, end, &output_len );
+    if( ret != 0 )
+        return( ret );
+
+    p += output_len;
+    MBEDTLS_PUT_UINT16_BE( p - p_extensions_len - 2, p_extensions_len, 0 );
+
+    *out_len = p - buf;
+
+    return( 0 );
+}
+
+static int ssl_tls13_write_certificate_request( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write certificate request" ) );
+
+    MBEDTLS_SSL_PROC_CHK_NEG( ssl_tls13_certificate_request_coordinate( ssl ) );
+
+    if( ret == SSL_CERTIFICATE_REQUEST_SEND_REQUEST )
+    {
+        unsigned char *buf;
+        size_t buf_len, msg_len;
+
+        MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_start_handshake_msg( ssl,
+                MBEDTLS_SSL_HS_CERTIFICATE_REQUEST, &buf, &buf_len ) );
+
+        MBEDTLS_SSL_PROC_CHK( ssl_tls13_write_certificate_request_body(
+                                  ssl, buf, buf + buf_len, &msg_len ) );
+
+        mbedtls_ssl_add_hs_msg_to_checksum(
+            ssl, MBEDTLS_SSL_HS_CERTIFICATE_REQUEST, buf, msg_len );
+
+        MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_finish_handshake_msg(
+                                  ssl, buf_len, msg_len ) );
+    }
+    else if( ret == SSL_CERTIFICATE_REQUEST_SKIP )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write certificate request" ) );
+        ret = 0;
+    }
+    else
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+        ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
+        goto cleanup;
+    }
+
+    mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_SERVER_CERTIFICATE );
+cleanup:
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write certificate request" ) );
+    return( ret );
+}
+#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
+
 /*
  * TLS 1.3 State Machine -- server side
  */
@@ -1195,6 +1320,12 @@
             }
             break;
 
+#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
+        case MBEDTLS_SSL_CERTIFICATE_REQUEST:
+            ret = ssl_tls13_write_certificate_request( ssl );
+            break;
+#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
+
         default:
             MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid state %d", ssl->state ) );
             return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 07ad1b3..591b6d3 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -11312,6 +11312,24 @@
             -s "=> parse client hello" \
             -s "<= parse client hello"
 
+requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_3
+requires_config_enabled MBEDTLS_DEBUG_C
+requires_config_enabled MBEDTLS_SSL_SRV_C
+requires_openssl_tls1_3
+run_test    "TLS 1.3: Server side check - openssl with client authentication" \
+            "$P_SRV debug_level=4 auth_mode=required crt_file=data_files/server5.crt key_file=data_files/server5.key force_version=tls13 tickets=0" \
+            "$O_NEXT_CLI -msg -debug -cert data_files/server5.crt -key data_files/server5.key -tls1_3" \
+            1 \
+            -s "tls13 server state: MBEDTLS_SSL_CLIENT_HELLO" \
+            -s "tls13 server state: MBEDTLS_SSL_SERVER_HELLO" \
+            -s "tls13 server state: MBEDTLS_SSL_ENCRYPTED_EXTENSIONS" \
+            -s "tls13 server state: MBEDTLS_SSL_CERTIFICATE_REQUEST" \
+            -s "tls13 server state: MBEDTLS_SSL_SERVER_CERTIFICATE" \
+            -s "=> write certificate request" \
+            -s "SSL - The requested feature is not available" \
+            -s "=> parse client hello" \
+            -s "<= parse client hello"
+
 requires_gnutls_tls1_3
 requires_gnutls_next_no_ticket
 requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_3
@@ -11329,6 +11347,25 @@
             -s "=> parse client hello" \
             -s "<= parse client hello"
 
+requires_gnutls_tls1_3
+requires_gnutls_next_no_ticket
+requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_3
+requires_config_enabled MBEDTLS_DEBUG_C
+requires_config_enabled MBEDTLS_SSL_SRV_C
+run_test    "TLS 1.3: Server side check - gnutls with client authentication" \
+            "$P_SRV debug_level=4 auth_mode=required crt_file=data_files/server5.crt key_file=data_files/server5.key force_version=tls13 tickets=0" \
+            "$G_NEXT_CLI localhost -d 4 --x509certfile data_files/server5.crt --x509keyfile data_files/server5.key --priority=NORMAL:-VERS-ALL:+VERS-TLS1.3:%NO_TICKETS:%DISABLE_TLS13_COMPAT_MODE -V" \
+            1 \
+            -s "tls13 server state: MBEDTLS_SSL_CLIENT_HELLO" \
+            -s "tls13 server state: MBEDTLS_SSL_SERVER_HELLO" \
+            -s "tls13 server state: MBEDTLS_SSL_ENCRYPTED_EXTENSIONS" \
+            -s "tls13 server state: MBEDTLS_SSL_CERTIFICATE_REQUEST" \
+            -s "tls13 server state: MBEDTLS_SSL_SERVER_CERTIFICATE" \
+            -s "=> write certificate request" \
+            -s "SSL - The requested feature is not available" \
+            -s "=> parse client hello" \
+            -s "<= parse client hello"
+
 requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_3
 requires_config_enabled MBEDTLS_DEBUG_C
 requires_config_enabled MBEDTLS_SSL_SRV_C
@@ -11341,6 +11378,24 @@
             -s "tls13 server state: MBEDTLS_SSL_SERVER_HELLO" \
             -s "tls13 server state: MBEDTLS_SSL_ENCRYPTED_EXTENSIONS" \
             -s "tls13 server state: MBEDTLS_SSL_SERVER_CERTIFICATE" \
+            -s "=> write certificate request" \
+            -c "client state: MBEDTLS_SSL_CERTIFICATE_REQUEST" \
+            -s "SSL - The requested feature is not available" \
+            -s "=> parse client hello" \
+            -s "<= parse client hello"
+
+requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_3
+requires_config_enabled MBEDTLS_DEBUG_C
+requires_config_enabled MBEDTLS_SSL_SRV_C
+requires_config_enabled MBEDTLS_SSL_CLI_C
+run_test    "TLS 1.3: Server side check - mbedtls with client authentication" \
+            "$P_SRV debug_level=4 auth_mode=required crt_file=data_files/server5.crt key_file=data_files/server5.key force_version=tls13 tickets=0" \
+            "$P_CLI debug_level=4 crt_file=data_files/server5.crt key_file=data_files/server5.key force_version=tls13" \
+            1 \
+            -s "tls13 server state: MBEDTLS_SSL_CLIENT_HELLO" \
+            -s "tls13 server state: MBEDTLS_SSL_SERVER_HELLO" \
+            -s "tls13 server state: MBEDTLS_SSL_ENCRYPTED_EXTENSIONS" \
+            -s "tls13 server state: MBEDTLS_SSL_SERVER_CERTIFICATE" \
             -c "client state: MBEDTLS_SSL_CERTIFICATE_REQUEST" \
             -s "SSL - The requested feature is not available" \
             -s "=> parse client hello" \