[Server] add XrdSecssh plugin with tests and packaging

Add the new TLS-only XrdSecssh security plugin with key, agent and
certificate support.

3on tokenizer buffer. Link test binary against OpenSSL::Crypto for new
3only ran during OpInit), remove unused rawPub field from TrustedKey,
3can drive the output length negative.
3Made-with: Cursor

3[Tests] Move XrdSecSSH tests to dedicated xrdsecssh-unit-tests target

Author: apeters1971

debian/xrootd-plugins.install

@@ -6,6 +6,7 @@
 /usr/lib/*/libXrdSecgsiAUTHZVO-5.so
 /usr/lib/*/libXrdSecgsiGMAPDN-5.so
 /usr/lib/*/libXrdSeckrb5-5.so
+/usr/lib/*/libXrdSecssh-5.so
 /usr/lib/*/libXrdSecpwd-5.so
 /usr/lib/*/libXrdSecsss-5.so
 /usr/lib/*/libXrdSecunix-5.so

python/docs/source/install.rst

@@ -166,6 +166,7 @@ In this case, the structure is a bit different than before::
   |   |-- libXrdSecgsiAUTHZVO-5.so
   |   |-- libXrdSecgsiGMAPDN-5.so
   |   |-- libXrdSeckrb5-5.so
+  |   |-- libXrdSecssh-5.so
   |   |-- libXrdSecpwd-5.so
   |   |-- libXrdSecsss-5.so
   |   |-- libXrdSecunix-5.so

src/CMakeLists.txt

@@ -55,6 +55,7 @@ add_subdirectory( XrdPosix )
 add_subdirectory( XrdSec )
 add_subdirectory( XrdSecgsi )
 add_subdirectory( XrdSeckrb5 )
+add_subdirectory( XrdSecssh )
 add_subdirectory( XrdSecpwd )
 add_subdirectory( XrdSecsss )
 add_subdirectory( XrdSecunix )

src/XrdSecssh/CMakeLists.txt

@@ -0,0 +1,8 @@
+set(XrdSecssh XrdSecssh-${PLUGIN_VERSION})
+
+find_package(OpenSSL REQUIRED)
+
+add_library(${XrdSecssh} MODULE XrdSecProtocolssh.cc)
+target_link_libraries(${XrdSecssh} PRIVATE XrdUtils OpenSSL::Crypto)
+
+install(TARGETS ${XrdSecssh} LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR})

src/XrdSecssh/README.md

@@ -0,0 +1,164 @@
+# XrdSecssh
+
+`XrdSecssh` is an experimental XRootD security protocol plugin (`sec.protocol ssh`)
+for SSH-key-based authentication over TLS.
+
+## V1 behavior
+
+- Raw key mode and OpenSSH user certificate mode
+- Server trust source:
+  - `keys-file` for raw key -> user mapping
+  - optional `ca-keys-file` for user certificate validation
+- Supported raw key algorithms: `ssh-ed25519`, `ssh-rsa`
+- Supported user certificate algorithms: `ssh-ed25519-cert-v01@openssh.com`,
+  `ssh-rsa-cert-v01@openssh.com`
+- Two-step handshake:
+  1. client sends user + SSH key/certificate blob
+  2. server sends nonce challenge
+  3. client signs challenge with private key
+  4. server verifies signature and maps to local username
+
+## Server configuration
+
+```conf
+sec.protocol ssh \
+  -keys-file /etc/xrootd/ssh_authorized_keys \
+  -ca-keys-file /etc/xrootd/ssh_ca_keys \
+  -principal-as-user \
+  -principal-map \
+  -maxsz 8192 \
+  -nonce-ttl 30 \
+  -debug
+```
+
+`keys-file` security checks:
+
+- must be a regular file
+- must be owned by effective xrootd uid
+- must not be group/other writable
+
+The same security checks apply to `ca-keys-file` when configured.
+The same security checks apply to `principal-map-file` when configured.
+
+### keys-file format
+
+Accepted line formats:
+
+1. Explicit user mapping:
+
+```text
+foo ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI...
+foo ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQ...
+```
+
+2. Authorized-keys style fallback mapping (username extracted from comment prefix before `@`):
+
+```text
+ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI... foo@host
+ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQ... foo@host
+```
+
+### ca-keys-file format (optional)
+
+Each line should contain a CA public key:
+
+```text
+ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI...
+ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQ...
+```
+
+Also accepted:
+
+```text
+cert-authority ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI...
+```
+
+When a user certificate is presented, the server validates:
+
+- certificate signature against trusted CA key
+- certificate type is user (`type=1`)
+- validity window (`valid_after` / `valid_before`)
+- principals contain requested user (if principals list is non-empty)
+
+### Principal mapping options (cert mode)
+
+Server options:
+
+- `-principal-as-user`:
+  map a certificate principal directly to local account if it is a valid
+  local username or uid.
+- `-principal-map`:
+  enable principal mapping file at default path (no argument)
+  `/etc/xrootd/ssh_principals.map`.
+- `-principal-map-file <path>`:
+  use a custom principal mapping file.
+
+If both direct and file mapping are enabled, direct principal->local-user
+mapping is tried first, then the map file.
+
+Map file format:
+
+```text
+principal-a alice
+principal-b 1001
+```
+
+Each line is `<principal> <username|uid>`.
+
+The principal map file is monitored during authentication and is reloaded
+automatically if its inode or mtime changes.
+
+## Client configuration
+
+Default mode uses a private key file (PEM/PKCS8 format; supported key types: ed25519, rsa):
+
+```sh
+export XRD_SSH_KEY_FILE=/path/to/ed25519-private.pem
+```
+
+Client `ssh-agent` mode is also supported:
+
+```sh
+export SSH_AUTH_SOCK=/run/user/1000/ssh-agent.socket
+export XRD_SSH_AGENT=1
+```
+
+When `XRD_SSH_AGENT=1`, the client picks a supported identity from the agent
+and signs the server challenge via agent.
+
+Supported agent identities:
+
+- raw keys: `ssh-ed25519`, `ssh-rsa`
+- user certificates: `ssh-ed25519-cert-v01@openssh.com`,
+  `ssh-rsa-cert-v01@openssh.com`
+
+Optional key selection by fingerprint:
+
+```sh
+export XRD_SSH_AGENT_FINGERPRINT='SHA256:base64fingerprint'
+```
+
+Fallback behavior:
+
+- if `XRD_SSH_AGENT` is not set, key-file mode is tried first
+- if key-file is not configured and `SSH_AUTH_SOCK` exists, agent mode is used
+- if not in agent mode, no key-file env is set, and `XRD_SSH_USER` is not set,
+  the client also tries default key files in order:
+  - `~/.ssh/id_ed25519`
+  - `~/.ssh/id_rsa`
+- if all methods fail, authentication fails with a detailed error
+
+Optional username override:
+
+```sh
+export XRD_SSH_USER=foo
+```
+
+If `XRD_SSH_USER` is not set, `USER` is used.
+
+## Notes
+
+- TLS is mandatory (`needTLS() == true`)
+- handshake nonce is single-use and expires after `-nonce-ttl`
+- debug logging can be enabled via `-debug` or `XrdSecDEBUG=1`; it prints
+  loaded key metadata (alg/user/fingerprint) and authentication key selection