Update documentation and rename the extra to "gssauth"

Author: eltoder

README.rst

@@ -58,11 +58,18 @@ This enables asyncpg to have easy-to-use support for:
 Installation
 ------------
 
-asyncpg is available on PyPI and has no dependencies.
-Use pip to install::
+asyncpg is available on PyPI.  When not using GSSAPI/SSPI authentication it
+has no dependencies.  Use pip to install::
 
     $ pip install asyncpg
 
+If you need GSSAPI/SSPI authentication, use::
+
+    $ pip install 'asyncpg[gssauth]'
+
+For more details, please `see the documentation
+<https://magicstack.github.io/asyncpg/current/installation.html>`_.
+
 
 Basic Usage
 -----------

asyncpg/protocol/coreproto.pyx

@@ -724,7 +724,7 @@ cdef class CoreProtocol:
             import gssapi
         except ModuleNotFoundError:
             raise apg_exc.InterfaceError(
-                'gssapi module not found; please install asyncpg[gssapi] to '
+                'gssapi module not found; please install asyncpg[gssauth] to '
                 'use asyncpg with Kerberos/GSSAPI/SSPI authentication'
             ) from None
 
@@ -736,7 +736,7 @@ cdef class CoreProtocol:
             import sspilib
         except ModuleNotFoundError:
             raise apg_exc.InterfaceError(
-                'sspilib module not found; please install asyncpg[gssapi] to '
+                'sspilib module not found; please install asyncpg[gssauth] to '
                 'use asyncpg with Kerberos/GSSAPI/SSPI authentication'
             ) from None
 

docs/installation.rst

@@ -4,20 +4,35 @@
 Installation
 ============
 
-**asyncpg** has no external dependencies and the recommended way to
-install it is to use **pip**:
+**asyncpg** has no external dependencies when not using GSSAPI/SSPI
+authentication.  The recommended way to install it is to use **pip**:
 
 .. code-block:: bash
 
     $ pip install asyncpg
 
+If you need GSSAPI/SSPI authentication, the recommended way is to use
 
-.. note::
+.. code-block:: bash
+
+    $ pip install 'asyncpg[gssauth]'
+
+This installs SSPI support on Windows and GSSAPI support on non-Windows
+platforms.  SSPI and GSSAPI interoperate as clients and servers: an SSPI
+client can authenticate to a GSSAPI server and vice versa.
+
+On Linux installing GSSAPI requires a working C compiler and Kerberos 5
+development files.  The latter can be obtained by installing **libkrb5-dev**
+package on Debian/Ubuntu or **krb5-devel** on RHEL/Fedora.  (This is needed
+because PyPI does not have Linux wheels for gssapi. See `here for the details
+<https://github.com/pythongssapi/python-gssapi/issues/200#issuecomment-1032934269>`_.)
+
+It is also possible to use GSSAPI on Windows:
 
-   It is recommended to use **pip** version **8.1** or later to take
-   advantage of the precompiled wheel packages.  Older versions of pip
-   will ignore the wheel packages and install asyncpg from the source
-   package.  In that case a working C compiler is required.
+  * `pip install gssapi`
+  * Install `Kerberos for Windows <https://web.mit.edu/kerberos/dist/>`_.
+  * Set the ``gsslib`` parameter or the ``PGGSSLIB`` environment variable to
+    `gssapi` when connecting.
 
 
 Building from source

pyproject.toml

@@ -35,7 +35,7 @@ dependencies = [
 github = "https://github.com/MagicStack/asyncpg"
 
 [project.optional-dependencies]
-gssapi = [
+gssauth = [
     'gssapi; platform_system != "Windows"',
     'sspilib; platform_system == "Windows"',
 ]