Add support for SSL client certificate (load_cert_chain)

Tested with badssl.com:

 1. Get client certificates from https://badssl.com/download/
 2. Convert public portion with `openssl x509 -in badssl.com-client.pem -out CIRCUITPY/cert.pem`
 3. Convert private portion with `openssl rsa -in badssl.com-client.pem -out CIRCUITPY/privkey.pem` and the password `badssl.com`
 4. Put wifi settings in CIRCUITPY/.env
 5. Run the below Python script:

```py
import os
import wifi
import socketpool
import ssl
import adafruit_requests

TEXT_URL = "https://client.badssl.com/"
wifi.radio.connect(os.getenv('WIFI_SSID'), os.getenv('WIFI_PASSWORD'))

pool = socketpool.SocketPool(wifi.radio)
context = ssl.create_default_context()
requests = adafruit_requests.Session(pool, context)

print(f"Fetching from {TEXT_URL} without certificate (should fail)")
response = requests.get(TEXT_URL)
print(f"{response.status_code=}, should be 400 Bad Request")
input("hit enter to continue\r")

print("Loading client certificate")
context.load_cert_chain("/cert.pem", "privkey.pem")
requests = adafruit_requests.Session(pool, context)

print(f"Fetching from {TEXT_URL} with certificate (should succeed)")
response = requests.get(TEXT_URL)
print(f"{response.status_code=}, should be 200 OK")
```

ports/espressif/common-hal/ssl/SSLContext.c

@@ -87,3 +87,10 @@ bool common_hal_ssl_sslcontext_get_check_hostname(ssl_sslcontext_obj_t *self) {
 void common_hal_ssl_sslcontext_set_check_hostname(ssl_sslcontext_obj_t *self, bool value) {
     self->ssl_config.skip_common_name = !value;
 }
+
+void common_hal_ssl_sslcontext_load_cert_chain(ssl_sslcontext_obj_t *self, mp_buffer_info_t *cert_buf, mp_buffer_info_t *key_buf) {
+    self->ssl_config.clientcert_buf = cert_buf->buf;
+    self->ssl_config.clientcert_bytes = cert_buf->len + 1;
+    self->ssl_config.clientkey_buf = key_buf->buf;
+    self->ssl_config.clientkey_bytes = key_buf->len + 1;
+}

ports/raspberrypi/common-hal/ssl/SSLContext.c

@@ -39,12 +39,10 @@ void common_hal_ssl_sslcontext_construct(ssl_sslcontext_obj_t *self) {
 
 void common_hal_ssl_sslcontext_load_verify_locations(ssl_sslcontext_obj_t *self,
     const char *cadata) {
-    mp_raise_NotImplementedError(NULL);
+    self->crt_bundle_attach = NULL;
-
+    self->use_global_ca_store = false;
-    // self->crt_bundle_attach = NULL;
+    self->cacert_buf = (const unsigned char *)cadata;
-    // self->use_global_ca_store = false;
+    self->cacert_bytes = strlen(cadata) + 1;
-    // self->cacert_buf = (const unsigned char *)cadata;
-    // self->cacert_bytes = strlen(cadata) + 1;
 }
 
 void common_hal_ssl_sslcontext_set_default_verify_paths(ssl_sslcontext_obj_t *self) {
@@ -61,3 +59,8 @@ bool common_hal_ssl_sslcontext_get_check_hostname(ssl_sslcontext_obj_t *self) {
 void common_hal_ssl_sslcontext_set_check_hostname(ssl_sslcontext_obj_t *self, bool value) {
     self->check_name = value;
 }
+
+void common_hal_ssl_sslcontext_load_cert_chain(ssl_sslcontext_obj_t *self, mp_buffer_info_t *cert_buf, mp_buffer_info_t *key_buf) {
+    self->cert_buf = *cert_buf;
+    self->key_buf = *key_buf;
+}

ports/raspberrypi/common-hal/ssl/SSLContext.h

@@ -36,4 +36,5 @@ typedef struct {
     const unsigned char *cacert_buf;
     size_t cacert_bytes;
     int (*crt_bundle_attach)(mbedtls_ssl_config *conf);
+    mp_buffer_info_t cert_buf, key_buf;
 } ssl_sslcontext_obj_t;

ports/raspberrypi/common-hal/ssl/SSLSocket.c

@@ -197,6 +197,21 @@ ssl_sslsocket_obj_t *common_hal_ssl_sslcontext_wrap_socket(ssl_sslcontext_obj_t
 
     mbedtls_ssl_set_bio(&o->ssl, &o->sock, _mbedtls_ssl_send, _mbedtls_ssl_recv, NULL);
 
+    if (self->cert_buf.buf != NULL) {
+        ret = mbedtls_pk_parse_key(&o->pkey, self->key_buf.buf, self->key_buf.len + 1, NULL, 0);
+        if (ret != 0) {
+            goto cleanup;
+        }
+        ret = mbedtls_x509_crt_parse(&o->cert, self->cert_buf.buf, self->cert_buf.len + 1);
+        if (ret != 0) {
+            goto cleanup;
+        }
+
+        ret = mbedtls_ssl_conf_own_cert(&o->conf, &o->cert, &o->pkey);
+        if (ret != 0) {
+            goto cleanup;
+        }
+    }
     return o;
 cleanup:
     mbedtls_pk_free(&o->pkey);

ports/raspberrypi/mbedtls/mbedtls_config.h

@@ -77,6 +77,7 @@
 #define MBEDTLS_AES_C
 #define MBEDTLS_ASN1_PARSE_C
 #define MBEDTLS_ASN1_WRITE_C
+#define MBEDTLS_BASE64_C
 #define MBEDTLS_BIGNUM_C
 #define MBEDTLS_CIPHER_C
 #define MBEDTLS_CTR_DRBG_C
@@ -90,6 +91,7 @@
 #define MBEDTLS_MD5_C
 #define MBEDTLS_OID_C
 #define MBEDTLS_PKCS5_C
+#define MBEDTLS_PEM_PARSE_C
 #define MBEDTLS_PK_C
 #define MBEDTLS_PK_PARSE_C
 #define MBEDTLS_PLATFORM_C

shared-bindings/ssl/SSLContext.c

@@ -27,6 +27,7 @@
 #include <stdio.h>
 #include <string.h>
 
+#include "extmod/vfs.h"
 #include "py/objtuple.h"
 #include "py/objlist.h"
 #include "py/objproperty.h"
@@ -52,6 +53,47 @@ STATIC mp_obj_t ssl_sslcontext_make_new(const mp_obj_type_t *type, size_t n_args
     return MP_OBJ_FROM_PTR(s);
 }
 
+//|     def load_cert_chain(self, certfile: str, keyfile: str) -> None:
+//|         """Load a private key and the corresponding certificate.
+//|
+//|         The certfile string must be the path to a single file in PEM format
+//|         containing the certificate as well as any number of CA certificates
+//|         needed to establish the certificate's authenticity.  The keyfile string
+//|         must point to a file containing the private key.
+//|         """
+
+STATIC void get_file_contents(mp_obj_t name_obj, mp_buffer_info_t *bufinfo) {
+    mp_obj_t file = mp_call_function_2(MP_OBJ_FROM_PTR(&mp_builtin_open_obj), name_obj, MP_OBJ_NEW_QSTR(MP_QSTR_rb));
+    mp_obj_t dest[2];
+    mp_load_method(file, MP_QSTR_read, dest);
+    mp_obj_t result = mp_call_method_n_kw(0, 0, dest);
+    mp_get_buffer_raise(result, bufinfo, MP_BUFFER_READ);
+}
+
+STATIC mp_obj_t ssl_sslcontext_load_cert_chain(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    enum { ARG_certfile, ARG_keyfile };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_certfile, MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = mp_const_none} },
+        { MP_QSTR_keyfile, MP_ARG_OBJ, {.u_obj = mp_const_none} },
+    };
+    ssl_sslcontext_obj_t *self = MP_OBJ_TO_PTR(pos_args[0]);
+
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+
+    mp_buffer_info_t cert_buf, key_buf;
+    get_file_contents(args[ARG_certfile].u_obj, &cert_buf);
+    if (args[ARG_keyfile].u_obj != mp_const_none) {
+        get_file_contents(args[ARG_keyfile].u_obj, &key_buf);
+    } else {
+        key_buf = cert_buf;
+    }
+
+    common_hal_ssl_sslcontext_load_cert_chain(self, &cert_buf, &key_buf);
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_KW(ssl_sslcontext_load_cert_chain_obj, 1, ssl_sslcontext_load_cert_chain);
+
 //|     def load_verify_locations(self, cadata: Optional[str] = None) -> None:
 //|         """Load a set of certification authority (CA) certificates used to validate
 //|         other peers' certificates."""
@@ -146,6 +188,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_KW(ssl_sslcontext_wrap_socket_obj, 1, ssl_sslcont
 
 STATIC const mp_rom_map_elem_t ssl_sslcontext_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_wrap_socket), MP_ROM_PTR(&ssl_sslcontext_wrap_socket_obj) },
+    { MP_ROM_QSTR(MP_QSTR_load_cert_chain), MP_ROM_PTR(&ssl_sslcontext_load_cert_chain_obj) },
     { MP_ROM_QSTR(MP_QSTR_load_verify_locations), MP_ROM_PTR(&ssl_sslcontext_load_verify_locations_obj) },
     { MP_ROM_QSTR(MP_QSTR_set_default_verify_paths), MP_ROM_PTR(&ssl_sslcontext_set_default_verify_paths_obj) },
     { MP_ROM_QSTR(MP_QSTR_check_hostname), MP_ROM_PTR(&ssl_sslcontext_check_hostname_obj) },

shared-bindings/ssl/SSLContext.h

@@ -46,5 +46,6 @@ void common_hal_ssl_sslcontext_set_default_verify_paths(ssl_sslcontext_obj_t *se
 
 bool common_hal_ssl_sslcontext_get_check_hostname(ssl_sslcontext_obj_t *self);
 void common_hal_ssl_sslcontext_set_check_hostname(ssl_sslcontext_obj_t *self, bool value);
+void common_hal_ssl_sslcontext_load_cert_chain(ssl_sslcontext_obj_t *self, mp_buffer_info_t *cert_buf, mp_buffer_info_t *key_buf);
 
 #endif // MICROPY_INCLUDED_SHARED_BINDINGS_SSL_SSLCONTEXT_H