vauth: Introduced Curl_auth_is_<mechansism>_supported() functions

As Windows SSPI authentication calls fail when a particular mechanism
isn't available, introduced these functions for DIGEST, NTLM, Kerberos 5
and Negotiate to allow both HTTP and SASL authentication the opportunity
to query support for a supported mechanism before selecting it.

For now each function returns TRUE to maintain compatability with the
existing code when called.

lib/vauth/digest.c

@@ -305,6 +305,20 @@ static CURLcode auth_decode_digest_md5_message(const char *chlg64,
   return CURLE_OK;
 }
 
+/*
+ * Curl_auth_is_digest_supported()
+ *
+ * This is used to evaluate if DIGEST is supported.
+ *
+ * Parameters: None
+ *
+ * Returns TRUE as DIGEST as handled by libcurl.
+ */
+bool Curl_auth_is_digest_supported(void)
+{
+  return TRUE;
+}
+
 /*
  * Curl_auth_create_digest_md5_message()
  *

lib/vauth/digest_sspi.c

@@ -43,6 +43,22 @@
 #include "curl_memory.h"
 #include "memdebug.h"
 
+/*
+* Curl_auth_is_digest_supported()
+*
+* This is used to evaluate if DIGEST is supported.
+*
+* Parameters: None
+*
+* Returns TRUE if DIGEST is supported by Windows SSPI.
+*/
+bool Curl_auth_is_digest_supported(void)
+{
+  /* TODO: Return true for now which maintains compatability with the existing
+     code */
+  return TRUE;
+}
+
 /*
  * Curl_auth_create_digest_md5_message()
  *

lib/vauth/krb5_gssapi.c

@@ -41,6 +41,20 @@
 #include "curl_memory.h"
 #include "memdebug.h"
 
+/*
+ * Curl_auth_is_gssapi_supported()
+ *
+ * This is used to evaluate if GSSAPI (Kerberos V5) is supported.
+ *
+ * Parameters: None
+ *
+ * Returns TRUE if Kerberos V5 is supported by the GSS-API library.
+ */
+bool Curl_auth_is_gssapi_supported(void)
+{
+  return TRUE;
+}
+
 /*
  * Curl_auth_create_gssapi_user_message()
  *

lib/vauth/krb5_sspi.c

@@ -39,6 +39,22 @@
 #include "curl_memory.h"
 #include "memdebug.h"
 
+/*
+ * Curl_auth_is_gssapi_supported()
+ *
+ * This is used to evaluate if GSSAPI (Kerberos V5) is supported.
+ *
+ * Parameters: None
+ *
+ * Returns TRUE if Kerberos V5 is supported by Windows SSPI.
+ */
+bool Curl_auth_is_gssapi_supported(void)
+{
+  /* TODO: Return true for now which maintains compatability with the existing
+     code */
+  return TRUE;
+}
+
 /*
  * Curl_auth_create_gssapi_user_message()
  *

lib/vauth/ntlm.c

@@ -216,6 +216,20 @@ static CURLcode ntlm_decode_type2_target(struct Curl_easy *data,
        from the beginning of the NTLM message.
 */
 
+/*
+ * Curl_auth_is_ntlm_supported()
+ *
+ * This is used to evaluate if NTLM is supported.
+ *
+ * Parameters: None
+ *
+ * Returns TRUE as NTLM as handled by libcurl.
+ */
+bool Curl_auth_is_ntlm_supported(void)
+{
+  return TRUE;
+}
+
 /*
  * Curl_auth_decode_ntlm_type2_message()
  *

lib/vauth/ntlm_sspi.c

@@ -37,6 +37,22 @@
 #include "curl_memory.h"
 #include "memdebug.h"
 
+/*
+ * Curl_auth_is_ntlm_supported()
+ *
+ * This is used to evaluate if NTLM is supported.
+ *
+ * Parameters: None
+ *
+ * Returns TRUE if NTLM is supported by Windows SSPI.
+ */
+bool Curl_auth_is_ntlm_supported(void)
+{
+  /* TODO: Return true for now which maintains compatability with the existing
+     code */
+  return TRUE;
+}
+
 /*
  * Curl_auth_create_ntlm_type1_message()
  *

lib/vauth/spnego_gssapi.c

@@ -40,6 +40,20 @@
 #include "curl_memory.h"
 #include "memdebug.h"
 
+/*
+ * Curl_auth_is_spnego_supported()
+ *
+ * This is used to evaluate if SPNEGO (Negotiate) is supported.
+ *
+ * Parameters: None
+ *
+ * Returns TRUE if Negotiate supported by the GSS-API library.
+ */
+bool Curl_auth_is_spnego_supported(void)
+{
+  return TRUE;
+}
+
 /*
  * Curl_auth_decode_spnego_message()
  *

lib/vauth/spnego_sspi.c

@@ -39,6 +39,22 @@
 #include "curl_memory.h"
 #include "memdebug.h"
 
+/*
+ * Curl_auth_is_spnego_supported()
+ *
+ * This is used to evaluate if SPNEGO (Negotiate) is supported.
+ *
+ * Parameters: None
+ *
+ * Returns TRUE if Negotiate is supported by Windows SSPI.
+ */
+bool Curl_auth_is_spnego_supported(void)
+{
+  /* TODO: Return true for now which maintains compatability with the existing
+     code */
+  return TRUE;
+}
+
 /*
  * Curl_auth_decode_spnego_message()
  *

lib/vauth/vauth.h

@@ -83,6 +83,9 @@ CURLcode Curl_auth_create_cram_md5_message(struct Curl_easy *data,
                                            const char *passwdp,
                                            char **outptr, size_t *outlen);
 
+/* This is used to evaluate if DIGEST is supported */
+bool Curl_auth_is_digest_supported(void);
+
 /* This is used to generate a base64 encoded DIGEST-MD5 response message */
 CURLcode Curl_auth_create_digest_md5_message(struct Curl_easy *data,
                                              const char *chlg64,
@@ -109,6 +112,9 @@ void Curl_auth_digest_cleanup(struct digestdata *digest);
 #endif /* !CURL_DISABLE_CRYPTO_AUTH */
 
 #if defined(USE_NTLM)
+/* This is used to evaluate if NTLM is supported */
+bool Curl_auth_is_ntlm_supported(void);
+
 /* This is used to generate a base64 encoded NTLM type-1 message */
 CURLcode Curl_auth_create_ntlm_type1_message(const char *userp,
                                              const char *passwdp,
@@ -140,6 +146,9 @@ CURLcode Curl_auth_create_oauth_bearer_message(struct Curl_easy *data,
                                                const char *bearer,
                                                char **outptr, size_t *outlen);
 #if defined(USE_KERBEROS5)
+/* This is used to evaluate if GSSAPI (Kerberos V5) is supported */
+bool Curl_auth_is_gssapi_supported(void);
+
 /* This is used to generate a base64 encoded GSSAPI (Kerberos V5) user token
    message */
 CURLcode Curl_auth_create_gssapi_user_message(struct Curl_easy *data,
@@ -165,6 +174,9 @@ void Curl_auth_gssapi_cleanup(struct kerberos5data *krb5);
 #endif /* USE_KERBEROS5 */
 
 #if defined(USE_SPNEGO)
+/* This is used to evaluate if SPNEGO (Negotiate) is supported */
+bool Curl_auth_is_spnego_supported(void);
+
 /* This is used to decode a base64 encoded SPNEGO (Negotiate) challenge
    message */
 CURLcode Curl_auth_decode_spnego_message(struct Curl_easy *data,