sip/auth: SHA-256 digest algorithm support

[sreimers]

Fixes baresip/baresip#3006

Based on this PR:
#180

[juha-h]

Thanks, tested against my SIP proxy and SHA-256 worked OK:

7:35:16.608#
TCP 192.168.80.215:39768 -> 192.168.80.215:5060
REGISTER sip:test.tutpro.com SIP/2.0
Via: SIP/2.0/TCP 192.168.80.215:39768;branch=z9hG4bK7b572126dbcd7ba2;rport
Contact: <sip:test-0x55a0985a9470@192.168.80.215:39768;transport=tcp>;expires=600;+sip.instance="<urn:uuid:9b21c1a8-dc58-a3d6-83d5-7be67cbe70ce>";q=0.5;reg-id=1
Max-Forwards: 70
Authorization: Digest username="test", realm="test.tutpro.com", nonce="ZiUjNGYlIgj2oWfgNirlAvhoI3l75iN58/OfYYbWcmZpIZ4YcPY+BCgCliOA", uri="sip:test.tutpro.com", response="57f13b8a41a9de02c889f5ac06a8f68d5f3d4f854793a3b96bbb8656c944b345", cnonce="adb3fde0c3d55418", qop=auth, nc=00000002, algorithm=SHA-256
Route: <sip:test.tutpro.com:5060;transport=tcp;lr>
To: <sip:test@test.tutpro.com>
From: "Test Account" <sip:test@test.tutpro.com>;tag=e28b54998bd5899b
Call-ID: 8358afd383d29500
CSeq: 47131 REGISTER
User-Agent: baresip v3.11.0 (x86_64/Linux)
Supported: gruu, outbound, path
Allow: INVITE,ACK,BYE,CANCEL,OPTIONS,NOTIFY,SUBSCRIBE,INFO,MESSAGE,UPDATE,REFER
Content-Length: 0


17:35:16.611#
TCP 192.168.80.215:5060 -> 192.168.80.215:39768
SIP/2.0 401 Unauthorized
Via: SIP/2.0/TCP 192.168.80.215:39768;branch=z9hG4bK7b572126dbcd7ba2;rport=39768;received=192.168.80.215
To: <sip:test@test.tutpro.com>;tag=8ab7da41edb07e5e798dd89feb609822.ecd6b501
From: "Test Account" <sip:test@test.tutpro.com>;tag=e28b54998bd5899b
Call-ID: 8358afd383d29500
CSeq: 47131 REGISTER
WWW-Authenticate: Digest realm="test.tutpro.com", nonce="ZiUlUGYlJCQSrIR7c79myuEXJQlPZoil8/OfYYbWcmZpIZ4YcPY+BCgCmSaA", qop="auth", stale=true, algorithm=SHA-256
Server: OpenSIPg SIP Proxy (5.8.1-0b01 (x86_64/linux))
Content-Length: 0


17:35:16.614#
TCP 192.168.80.215:39768 -> 192.168.80.215:5060
REGISTER sip:test.tutpro.com SIP/2.0
Via: SIP/2.0/TCP 192.168.80.215:39768;branch=z9hG4bK2b3d137e373796f1;rport
Contact: <sip:test-0x55a0985a9470@192.168.80.215:39768;transport=tcp>;expires=600;+sip.instance="<urn:uuid:9b21c1a8-dc58-a3d6-83d5-7be67cbe70ce>";q=0.5;reg-id=1
Max-Forwards: 70
Authorization: Digest username="test", realm="test.tutpro.com", nonce="ZiUlUGYlJCQSrIR7c79myuEXJQlPZoil8/OfYYbWcmZpIZ4YcPY+BCgCmSaA", uri="sip:test.tutpro.com", response="f99b395637adef79ac457f7b27db8f070762c605e6faf641c1ff2135a2a96986", cnonce="591d20b93850ffbb", qop=auth, nc=00000001, algorithm=SHA-256
Route: <sip:test.tutpro.com:5060;transport=tcp;lr>
To: <sip:test@test.tutpro.com>
From: "Test Account" <sip:test@test.tutpro.com>;tag=e28b54998bd5899b
Call-ID: 8358afd383d29500
CSeq: 47132 REGISTER
User-Agent: baresip v3.11.0 (x86_64/Linux)
Supported: gruu, outbound, path
Allow: INVITE,ACK,BYE,CANCEL,OPTIONS,NOTIFY,SUBSCRIBE,INFO,MESSAGE,UPDATE,REFER
Content-Length: 0


17:35:16.630#
TCP 192.168.80.215:5060 -> 192.168.80.215:39768
SIP/2.0 200 OK
Via: SIP/2.0/TCP 192.168.80.215:39768;branch=z9hG4bK2b3d137e373796f1;rport=39768;received=192.168.80.215
To: <sip:test@test.tutpro.com>;tag=8ab7da41edb07e5e798dd89feb609822.754bb501
From: "Test Account" <sip:test@test.tutpro.com>;tag=e28b54998bd5899b
Call-ID: 8358afd383d29500
CSeq: 47132 REGISTER
Contact: <sip:test-0x55a0985a9470@192.168.80.215:39768;transport=tcp>;q=0.5;expires=600;received="sip:192.168.80.215:39768;transport=tcp";pub-gruu="sip:test@test.tutpro.com;gr=urn:uuid:9b21c1a8-dc58-a3d6-83d5-7be67cbe70ce";temp-gruu="sip:uloc-66252203-8a1e-1-d00c1e4e@test.tutpro.com;gr";+sip.instance="<urn:uuid:9b21c1a8-dc58-a3d6-83d5-7be67cbe70ce>";reg-id=1
Supported: outbound
Require: outbound
Server: OpenSIPg SIP Proxy (5.8.1-0b01 (x86_64/linux))
Content-Length: 0