Add sbom format to buildpacks toml

Signed-off-by: Sambhav Kothari <[email protected]>

text/0000-sbom.md

@@ -64,6 +64,23 @@ The motivation for supporting multiple SBOM formats is because there is currentl
 Currently the SBOM is defined in the `<layer>.toml`, `launch.toml` and `build.toml` respectively under the `[bom]` table.
 It may not be the most user-friendly way for buildpack authors to create SBOM documents in the above format. This RFC proposes that the `bom` be moved to `<layer>.bom.<ext>`, `launch.bom.<ext>` and `build.bom.<ext>` instead where `<ext>` will be `cdx.json` for CycloneDX documents and `spdx.json` for SPDX documents. A buildpack can also output the `bom` in multiple formats i.e. both CycloneDX and SPDX. 
 
+Additionally the buildpack must also indicate the SBOM format(s) it exports using the in its `buildapck.toml`'s `sbom` key in the `buildpacks` table.
+
+The format of this key should look like - 
+
+```toml
+api = "0.x"
+
+[buildpack]
+id = "<buildpack ID>"
+name = "<buildpack name>"
+# This can be an array of supported SBOM formats by the buildpack.
+# Valid array values are "CycloneDX" and "SPDX" as of this RFC.
+sbom = ["CycloneDX"]
+```
+
+This information can be displayed on the registry and `pack inspect-buildpack`.
+
 The lifecycle of the respective `bom` files during rebuilds would be exactly the same as the `bom` table currently. 
 
 The lifecycle would be responsible for taking all of the above `bom` files, and putting them in `/layers/config/sbom/<buildpack-id>/<layer-id>/<type>.bom.<ext>` for the layer `bom` files where `type` call be `build` or `launch` or `both`. Buildpack level BOM files will reside at `/layers/config/sbom/<buildpack-id>/build.bom.<ext>` and `/layers/config/sbom/<buildpack-id>/launch.bom.<ext>` for the `launch` and `build` `bom` respectively.
@@ -74,6 +91,7 @@ Merging different formats (CycloneDX/SPDX/Legacy CNB format) is a non-goal and w
 
 Since we will be preserving the original output files and if a buildpack chooses to output in both SPDX and CycloneDX, the lifecycle may eventually add support for SPDX merging in a future version if merging SPDX documents becomes better defined/efficient.
 
+
 # How it Works
 [how-it-works]: #how-it-works