Add 'sigalgs=' method for setting accepted signature algorithms

This adds OpenSSL::SSL::SSLContext#sigalgs= method and according unit tests
to provide access to the OpenSSL SSL_CTX_set1_sigalgs_list() method.
Using this method, authentication signature algorithms can be configured.

ext/openssl/extconf.rb

@@ -195,6 +195,7 @@ def find_openssl_library
 have_func("EVP_PKEY_check(NULL)", evp_h)
 have_func("EVP_PKEY_new_raw_private_key(0, NULL, (unsigned char *)\"\", 0)", evp_h)
 have_func("SSL_CTX_set_ciphersuites(NULL, \"\")", ssl_h)
+have_func("SSL_CTX_set1_sigalgs(NULL, NULL, 0L)", ssl_h)
 
 # added in 3.0.0
 have_func("SSL_set0_tmp_dh_pkey(NULL, NULL)", ssl_h)

ext/openssl/ossl_ssl.c

@@ -1103,6 +1103,36 @@ ossl_sslctx_set_ciphersuites(VALUE self, VALUE v)
 }
 #endif
 
+#ifdef HAVE_SSL_CTX_SET1_SIGALGS
+/*
+ * call-seq:
+ *    ctx.sigalgs = sigalgs_list -> sigalgs_list
+ *
+ * Sets the list of "supported signature algorithms" for this context.
+ *
+ * For a TLS client, the list is directly used in the supported
+ * signature algorithm list in the client hello message. For a server,
+ * the list is used by OpenSSL to determine the set of shared signature
+ * algorithms. OpenSSL will pick the most appropriate one from it.
+ */
+static VALUE
+ossl_sslctx_set_sigalgs(VALUE self, VALUE v)
+{
+    SSL_CTX *ctx;
+
+    if (NIL_P(v))
+        return v;
+
+    rb_check_frozen(self);
+    GetSSLCTX(self, ctx);
+
+    if (!SSL_CTX_set1_sigalgs_list(ctx, StringValueCStr(v)))
+        ossl_raise(eSSLError, "SSL_CTX_set1_sigalgs_list");
+
+    return v;
+}
+#endif
+
 #ifndef OPENSSL_NO_DH
 /*
  * call-seq:
@@ -2898,6 +2928,9 @@ Init_ossl_ssl(void)
 #ifdef HAVE_SSL_CTX_SET_CIPHERSUITES
     rb_define_method(cSSLContext, "ciphersuites=", ossl_sslctx_set_ciphersuites, 1);
 #endif
+#ifdef HAVE_SSL_CTX_SET1_SIGALGS
+    rb_define_method(cSSLContext, "sigalgs=", ossl_sslctx_set_sigalgs, 1);
+#endif
 #ifndef OPENSSL_NO_DH
     rb_define_method(cSSLContext, "tmp_dh=", ossl_sslctx_set_tmp_dh, 1);
 #endif

test/openssl/test_ssl.rb

@@ -1755,6 +1755,36 @@ def test_ciphers_method_tls_connection
     end
   end
 
+  def test_sigalgs_method_nil_argument
+    ssl_ctx = OpenSSL::SSL::SSLContext.new
+    pend 'sigalgs= method is missing' unless ssl_ctx.respond_to?(:sigalgs=)
+
+    assert_nothing_raised { ssl_ctx.sigalgs = nil }
+  end
+
+  def test_sigalgs_method_frozen_object
+    ssl_ctx = OpenSSL::SSL::SSLContext.new
+    pend 'sigalgs= method is missing' unless ssl_ctx.respond_to?(:sigalgs=)
+
+    ssl_ctx.freeze
+    assert_raise(FrozenError) { ssl_ctx.sigalgs = '"ECDSA+SHA256:RSA+SHA256"' }
+  end
+
+  def test_sigalgs_method_valid_sigalgs
+    ssl_ctx = OpenSSL::SSL::SSLContext.new
+    pend 'sigalgs= method is missing' unless ssl_ctx.respond_to?(:sigalgs=)
+
+    ssl_ctx.freeze
+    assert_raise(FrozenError) { ssl_ctx.sigalgs = '"ECDSA+SHA256:RSA+SHA256"' }
+  end
+
+  def test_sigalgs_method_bogus_sigalgs
+    ssl_ctx = OpenSSL::SSL::SSLContext.new
+    pend 'sigalgs= method is missing' unless ssl_ctx.respond_to?(:sigalgs=)
+
+    assert_raise(OpenSSL::SSL::SSLError) { ssl_ctx.sigalgs = 'BOGUS' }
+  end
+
   def test_ciphers_method_nil_argument
     ssl_ctx = OpenSSL::SSL::SSLContext.new
     assert_nothing_raised { ssl_ctx.ciphers = nil }