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, 29 insertions, 0 deletions

diff --git a/tests/extmod/ssl_sslcontext_ciphers.py b/tests/extmod/ssl_sslcontext_ciphers.py
new file mode 100644
index 0000000000..d87e96afdf
--- /dev/null
+++ b/tests/extmod/ssl_sslcontext_ciphers.py
@@ -0,0 +1,29 @@
+# Basic test of ssl.SSLContext get_ciphers() and set_ciphers() methods.
+
+try:
+    import ssl
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+
+ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
+
+ciphers = ctx.get_ciphers()
+
+for ci in ciphers:
+    print(ci)
+
+ctx.set_ciphers(ciphers[:1])
+
+# Test error cases.
+
+try:
+    ctx.set_ciphers(ciphers[0])
+except TypeError as e:
+    print(e)
+
+try:
+    ctx.set_ciphers(["BAR"])
+except OSError as e:
+    print(e)