feat(sql): Add URL safe base64 encoding function

This adds a SQL function to encode binary data into the URL safe base64
encoding defined in RFC 4648.

internal/db/schema/migrations/oss/postgres/80/01_history_domain.up.sql

@@ -0,0 +1,19 @@
+-- Copyright (c) HashiCorp, Inc.
+-- SPDX-License-Identifier: MPL-2.0
+
+begin;
+
+  -- Encodes binary data into URL safe base64 as specified in RFC 4648 Section 5.
+  -- See https://www.rfc-editor.org/rfc/rfc4648.html#section-5
+  create function wt_encode_base64_url_safe(bytes bytea) returns text
+  as $$
+    select rtrim(replace(replace(encode(bytes, 'base64'), '/', '_'), '+', '-'), '=');
+  $$ language sql
+     immutable
+     parallel safe -- all of the functions called are parallel safe
+     cost 1        -- all of the functions called are cost 1
+     strict;       -- means the function returns null on null input
+  comment on function wt_encode_base64_url_safe is
+    'Encodes binary data into URL safe base64';
+
+commit;

internal/db/sqltest/Makefile

@@ -29,6 +29,7 @@ TESTS ?= tests/setup/*.sql \
 		 tests/hcp/*/*.sql \
 		 tests/kms/*.sql \
 		 tests/plugin/*.sql \
+		 tests/history/*.sql \
 		 tests/recording/*.sql
 
 POSTGRES_DOCKER_IMAGE_BASE ?= postgres

internal/db/sqltest/tests/history/wt_encode_base64_url_safe.sql

@@ -0,0 +1,37 @@
+-- Copyright (c) HashiCorp, Inc.
+-- SPDX-License-Identifier: MPL-2.0
+
+begin;
+  select plan(6);
+
+  -- Verify the function exists and is declared properly
+  select has_function('wt_encode_base64_url_safe', array['bytea']);
+  select volatility_is('wt_encode_base64_url_safe', 'immutable');
+  select is_strict('wt_encode_base64_url_safe');
+
+  -- There are 3 differences between regular base64 and URL safe base64:
+  --  1. the '_' character is used in place of '/'
+  --  2. the '-' character is used in place of '+'
+  --  3. trailing '=' characters used for padding are removed
+  --
+  --    See https://www.rfc-editor.org/rfc/rfc4648.html#section-5
+  --
+  -- We only need to test these three changes since wt_encode_base64_url_safe
+  -- uses PostgreSQL's native encode function to encode the input into standard
+  -- base64.
+  --
+  -- The input for this test was found at https://commons.apache.org/proper/commons-codec/xref-test/org/apache/commons/codec/binary/Base64Test.html
+  --
+  -- The regular base64 encoding of the binary data encoded in the hex string '2bf7cc2701fe4397b49ebeed5acc7090'
+  -- is 'K/fMJwH+Q5e0nr7tWsxwkA==' which contains the '/', '+', and '='
+  -- characters, making it the perfect test case.
+  --
+  -- Validate this truely is the perfect test case
+  select is(encode('\x2bf7cc2701fe4397b49ebeed5acc7090'::bytea, 'base64'), 'K/fMJwH+Q5e0nr7tWsxwkA==');
+  -- Now test our function
+  select is(wt_encode_base64_url_safe('\x2bf7cc2701fe4397b49ebeed5acc7090'::bytea), 'K_fMJwH-Q5e0nr7tWsxwkA');
+  -- Verify the 'returns null on null input' is correct
+  select is(wt_encode_base64_url_safe(null), null);
+
+  select * from finish();
+rollback;