hostapd: add support for subject validation

hostapd: add support for subject validation

The wpa_supplicant supports certificate subject validation via the
subject match(2) and altsubject_match(2) fields. domain_match(2) and
domain_suffix_match(2) fields are also supported for advanced matches.
This validation is especially important when connecting to access
points that use PAP as the Phase 2 authentication type. Without proper
validation, the user's password can be transmitted to a rogue access
point in plaintext without the user's knowledge. Most organizations
already require these attributes to be included to ensure that the
connection from the STA and the AP is secure. Includes LuCI changes via
openwrt/luci#3444.

From the documentation:

subject_match - Constraint for server certificate subject. This substring
is matched against the subject of the authentication server certificate.
If this string is set, the server sertificate is only accepted if it
contains this string in the subject. The subject string is in following
format: /C=US/ST=CA/L=San Francisco/CN=Test AS/emailAddress=as
.example.com

subject_match2 - Constraint for server certificate subject. This field is
like subject_match, but used for phase 2 (inside EAP-TTLS/PEAP/FAST
tunnel) authentication.

altsubject_match - Constraint for server certificate alt. subject.
Semicolon separated string of entries to be matched against the
alternative subject name of the authentication server certificate. If
this string is set, the server sertificate is only accepted if it
contains one of the entries in an alternative subject name extension.
altSubjectName string is in following format: TYPE:VALUE Example:
EMAIL:server@example.com Example:
DNS:server.example.com;DNS:server2.example.com Following types are
supported: EMAIL, DNS, URI

altsubject_match2 - Constraint for server certificate alt. subject. This
field is like altsubject_match, but used for phase 2 (inside
EAP-TTLS/PEAP/FAST tunnel) authentication.

domain_match - Constraint for server domain name. If set, this FQDN is
used as a full match requirement for the
server certificate in SubjectAltName dNSName element(s). If a
matching dNSName is found, this constraint is met. If no dNSName
values are present, this constraint is matched against SubjectName CN
using same full match comparison. This behavior is similar to
domain_suffix_match, but has the requirement of a full match, i.e.,
no subdomains or wildcard matches are allowed. Case-insensitive
comparison is used, so "Example.com" matches "example.com", but would
not match "test.Example.com". More than one match string can be
provided by using semicolons to
separate the strings (e.g., example.org;example.com). When multiple
strings are specified, a match with any one of the values is considered
a sufficient match for the certificate, i.e., the conditions are ORed
together.

domain_match2 - Constraint for server domain name. This field is like
domain_match, but used for phase 2 (inside EAP-TTLS/PEAP/FAST tunnel)
authentication.

domain_suffix_match - Constraint for server domain name. If set, this
FQDN is used as a suffix match requirement for the AAA server
certificate in SubjectAltName dNSName element(s). If a matching dNSName
is found, this constraint is met. If no dNSName values are present,
this constraint is matched against SubjectName CN using same suffix
match comparison. Suffix match here means that the host/domain name is
compared one label at a time starting from the top-level domain and all
the labels in domain_suffix_match shall be included in the certificate.
The certificate may include additional sub-level labels in addition to
the required labels. More than one match string can be provided by using
semicolons to separate the strings (e.g., example.org;example.com).
When multiple strings are specified, a match with any one of the values
is considered a sufficient match for the certificate, i.e., the
conditions are ORed together. For example,
domain_suffix_match=example.com would match test.example.com but would
not match test-example.com. This field is like domain_match, but used
for phase 2 (inside EAP-TTLS/PEAP/FAST tunnel) authentication.

domain_suffix_match2 - Constraint for server domain name. This field is
like domain_suffix_match, but used for phase 2 (inside
EAP-TTLS/PEAP/FAST tunnel) authentication.

Signed-off-by: David Lam <david@thedavid.net>