add set0_rsa_oaep_label binding (#3894)

diff --git a/src/_cffi_src/openssl/rsa.py b/src/_cffi_src/openssl/rsa.py
index eddde84..459d5cb 100644
--- a/src/_cffi_src/openssl/rsa.py
+++ b/src/_cffi_src/openssl/rsa.py
@@ -21,6 +21,7 @@
 
 static const int Cryptography_HAS_PSS_PADDING;
 static const int Cryptography_HAS_RSA_OAEP_MD;
+static const int Cryptography_HAS_RSA_OAEP_LABEL;
 """
 
 FUNCTIONS = """
@@ -62,6 +63,7 @@
 int EVP_PKEY_CTX_set_rsa_padding(EVP_PKEY_CTX *, int);
 int EVP_PKEY_CTX_set_rsa_pss_saltlen(EVP_PKEY_CTX *, int);
 int EVP_PKEY_CTX_set_rsa_mgf1_md(EVP_PKEY_CTX *, EVP_MD *);
+int EVP_PKEY_CTX_set0_rsa_oaep_label(EVP_PKEY_CTX *, unsigned char *, int);
 
 int EVP_PKEY_CTX_set_rsa_oaep_md(EVP_PKEY_CTX *, EVP_MD *);
 """
@@ -76,6 +78,14 @@
 int (*EVP_PKEY_CTX_set_rsa_oaep_md)(EVP_PKEY_CTX *, EVP_MD *) = NULL;
 #endif
 
+#if defined(EVP_PKEY_CTX_set0_rsa_oaep_label)
+static const long Cryptography_HAS_RSA_OAEP_LABEL = 1;
+#else
+static const long Cryptography_HAS_RSA_OAEP_LABEL = 0;
+int (*EVP_PKEY_CTX_set0_rsa_oaep_label)(EVP_PKEY_CTX *, unsigned char *,
+                                        int) = NULL;
+#endif
+
 /* These functions were added in OpenSSL 1.1.0-pre5 (beta2) */
 #if CRYPTOGRAPHY_OPENSSL_LESS_THAN_110PRE5
 int RSA_set0_key(RSA *r, BIGNUM *n, BIGNUM *e, BIGNUM *d)
diff --git a/src/cryptography/hazmat/bindings/openssl/_conditional.py b/src/cryptography/hazmat/bindings/openssl/_conditional.py
index 7f61ed4..8eb6776 100644
--- a/src/cryptography/hazmat/bindings/openssl/_conditional.py
+++ b/src/cryptography/hazmat/bindings/openssl/_conditional.py
@@ -75,6 +75,12 @@
     ]
 
 
+def cryptography_has_rsa_oaep_label():
+    return [
+        "EVP_PKEY_CTX_set0_rsa_oaep_label",
+    ]
+
+
 def cryptography_has_ssl3_method():
     return [
         "SSLv3_method",
@@ -251,6 +257,7 @@
         cryptography_has_rsa_r_pkcs_decoding_error
     ),
     "Cryptography_HAS_RSA_OAEP_MD": cryptography_has_rsa_oaep_md,
+    "Cryptography_HAS_RSA_OAEP_LABEL": cryptography_has_rsa_oaep_label,
     "Cryptography_HAS_SSL3_METHOD": cryptography_has_ssl3_method,
     "Cryptography_HAS_ALPN": cryptography_has_alpn,
     "Cryptography_HAS_COMPRESSION": cryptography_has_compression,