extmod/modssl_mbedtls: Add SSLContext certificate methods.

This commit adds:

1) Methods to SSLContext class that match CPython signature:

	- `SSLContext.load_cert_chain(certfile, keyfile)`
	- `SSLContext.load_verify_locations(cafile=, cadata=)`
	- `SSLContext.get_ciphers()` --> ["CIPHERSUITE"]
	- `SSLContext.set_ciphers(["CIPHERSUITE"])`

2) `sslsocket.cipher()` to get current ciphersuite and protocol
   version.

3) `ssl.MBEDTLS_VERSION` string constant.

4) Certificate verification errors info instead of
   `MBEDTLS_ERR_X509_CERT_VERIFY_FAILED`.

5) Tests in `net_inet` and `multi_net` to test these new methods.

`SSLContext.load_cert_chain` method allows loading key and cert from disk
passing a filepath in `certfile` or `keyfile` options.

`SSLContext.load_verify_locations`'s `cafile` option enables the same
functionality for ca files.

Signed-off-by: Carlos Gil <carlosgilglez@gmail.com>

1 files changed, 58 insertions, 0 deletions

diff --git a/tests/multi_net/sslcontext_server_client_ciphers.py b/tests/multi_net/sslcontext_server_client_ciphers.py
new file mode 100644
index 0000000000..e2de4e6ad4
--- /dev/null
+++ b/tests/multi_net/sslcontext_server_client_ciphers.py
@@ -0,0 +1,58 @@
+# Test creating an SSL connection with specified ciphers.
+
+try:
+    import os
+    import socket
+    import ssl
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+PORT = 8000
+
+# These are test certificates. See tests/README.md for details.
+cert = cafile = "multi_net/rsa_cert.der"
+key = "multi_net/rsa_key.der"
+
+try:
+    os.stat(cafile)
+    os.stat(key)
+except OSError:
+    print("SKIP")
+    raise SystemExit
+
+
+# Server
+def instance0():
+    multitest.globals(IP=multitest.get_network_ip())
+    s = socket.socket()
+    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    s.bind(socket.getaddrinfo("0.0.0.0", PORT)[0][-1])
+    s.listen(1)
+    multitest.next()
+    s2, _ = s.accept()
+    server_ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
+    server_ctx.load_cert_chain(cert, key)
+    s2 = server_ctx.wrap_socket(s2, server_side=True)
+    assert isinstance(s2.cipher(), tuple)
+    print(s2.read(16))
+    s2.write(b"server to client")
+    s2.close()
+    s.close()
+
+
+# Client
+def instance1():
+    multitest.next()
+    s = socket.socket()
+    s.connect(socket.getaddrinfo(IP, PORT)[0][-1])
+    client_ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
+    ciphers = client_ctx.get_ciphers()
+    assert "TLS-RSA-WITH-AES-256-CBC-SHA256" in ciphers
+    client_ctx.set_ciphers(["TLS-RSA-WITH-AES-256-CBC-SHA256"])
+    client_ctx.verify_mode = ssl.CERT_REQUIRED
+    client_ctx.load_verify_locations(cafile=cafile)
+    s = client_ctx.wrap_socket(s, server_hostname="micropython.local")
+    s.write(b"client to server")
+    print(s.read(16))
+    s.close()